This has been a monero marketing point for a long time. To some extent I think it's kind of pointless navel gazing.
Imagine a currency that was perpetually inflationary by having everyone's holdings equally increase by 10% every year. Other than some logistic impacts with pricing and contract terms and some psychological effect, this would be a complete economic no-op: no one would be richer or poorer because of it. The "inflation" isn't what matters economically, what matters economically is how the inflation is distributed.
In light of that, I feel that the answer given by Todd and Monero promoters is answering the wrong question. When people are concerned about inflation they're really concerned about two things: Inflation unpredictability/uncertain, because unpredictable inflation can't be efficiently compensated for, and the cantillon effect-- the fact that the normal ways of creating inflation enrich parties close to the source of the money at the expense of the rest of the economy.
My toy example lacks both those issues: since it's predictable and everyone is proportional 'close' to the new money, which is why it's an economic no-op even though it is "infinite inflation". By contrast "
nocturnal[1]tail emission" fails both of those criteria and so it has an economic impact even if you accept that the argument that the supply of circulating coins is finite. ... a conclusion that shouldn't be at all surprising since if it has no economic effect no one would argue for it to begin with: having an economic effect is the point.
([1] Aside, the fact that many altcoins have been created by eastern Europeans seems to have resulted in using the word 'emission' instead of 'subsidy', but the word in the singular form is very uncommon in American English (rather than 'emissions', which is more common). For many people the immediate sophomoric association is the titter inducing "
nocturnal emission". Advocates of these schemes would do themselves a favor to call it "tail subsidy" instead as subsidy was the established term for the ex nihilo mining reward before altcoins started calling it 'emission'. I think it's more economically honest too-- as it is indisputably subsidy, and advocates for it ought to be explaining why miners need to be subsidized)
So any discussion of it should really be about the economic effect and its merits or harms-- the discussion about an "infinite" circulating supply is just a pure red herring.
But I'll embrace the red herring for a bit to highlight some of its limitations:
The convergent inflation argument has some striking similarities with Rizun's "A Transaction Fee Market Exists Without a Block Size Limit", in which Rizun effectively argues that Bitcoin there is some block size where the marginal increase in orphaning risk for a transaction makes it unattractive to add transactions paying under some threshold fee.
Rizun's argument is known to be fallacious due to its assumption that there is a marginal increase in orphaning risk. But any such risk is a technical artifact in how blocks are propagated and validated by miners and can be made arbitrarily low by centralizing mining or even eliminated completely by changing how block propagation works (and there are concrete schemes described that accomplish this).
Similarly, the convergent inflation argument assumes there is some consistent coin loss-- but that isn't a fundamental property of the system! One could easily imagine a future where long lived entities like states offer people payments (or discounts) if they encumber their coins with CSV-like releases if they go 1-2 lifetimes without being moved. In such a future coin loss could become arbitrarily small, maybe even effectively zero (if, e.g. standardness rules were put in place to avoid accidental losses). In some hyperbitconized future it would make a lot of sense for things to move in this direction.
(At one point I even drafted up a mailing list posts suggesting that Bitcoin core should consider offering an option for people to dedicate their long lost coins to development help fund future development, but never finished it because I figured it would generate too much drama for the amount of benefit it would provide.)
Rizun's argument is also flawed in that at best it only makes a case that an equilibrium exists (and it also requires endless mining subsidy, but I'll ignore that), not that that the equilibrium is an acceptable one: It might only be achieved at transaction levels far beyond any conceivable demand or only at a level where the computational costs of running a node would be unreachable by practically anyone. The convergent inflation argument is somewhat better in that it seems clear that the equilibrium would
eventually be reached (where Rizun's doesn't even achieve that), but the equilibrium point might further out than the lifespan of our sun.
Unlike Rizun's argument I don't think these points are strong enough to demolish the idea that continued subsidy could be convergent entirely, but I think they do point out limits in the argument.
But as I said above, I think the argument that the supply of circulating coins converges is really a red herring. Instead, we should consider the economic effects:
Is it desirable, much less moral, for a percentage of the world's wealth be continually diverted to support mining? I wouldn't take an absolute hard line position that it wasn't desirable, or even that it wouldn't be moral (at least in so far as it was a system people consented to use)-- but the reasonableness of this depends critically on the
amount. Would 0.001% be acceptable? I suppose! would 10%? Absolutely not. And here the convergence from loss argument actually makes a case against the policy it intends to support: It admits and depends on uncertain coin loss, but by that same token we can't know the rate. It's completely credible that after some major war or disaster that suddenly a large percentage of coins could be lost at once (particularly if the above mentioned recovery schemes hadn't been widely implemented yet). If that happens the "transitory" inflation might become extremely market distorting, ultimately harming civilization by directing an unconscionable share of resources to mining or (more likely) causing the system to be abandoned.
I think it's also worth considering that the total supply of non-lost coins and the circulating economy are quite distinct things. Our civilization has undergone a couple centuries of tremendous sustained growth as a result of technologies such as fossil fuel and the haber process-- and I think it may be giving us a rather biased perspective on the dynamics of mankind's economies in the far future: There are straightforward thermodynamic reasons that an expansion of our economy (much less an accelerating expansion) shouldn't be expected for indefinitely long time. Even if you assume we'll someday populate the stars, absent new physics that makes FTL travel possible, the size of an interconnected economy is finite (though perhaps quite large!). Fanciful speculation aside, even in our current economy we go through periods of higher and lower activity, and so if the miner's income doesn't depend on the current circulating economy (which could be a fraction of the stashed wealth) it could easily become distortingly large during slow periods-- which should be common in a less expansionary economy (and may last generations!).
The uncertainty of the amount works in the other direction too: Continued subsidy isn't guaranteed to be enough to support security in any meaningful sense, it could be too small to achieve its intended goal as well as too large. Because of economic cycles the same scheme could even be both, disruptively overpaying during economic slumps (diverting resources to excess security) and disastrously underpaying during economic booms (failing to achieve the security goals). Without thinking carefully you might think that sometimes underpaying would still be better than zero subsidy but that isn't clear to me because unpredictability in security is itself a problem because it interferes with compensating behaviors.
With these points in mind I think Satoshi made a very good decision. Bitcoin's tail subsidy scheme of zero is the unique amount of tail subsidy guaranteed to (eventually) never overpay. It is the value with the minimum amount of economic uncertainty, excluding security considerations. It does make a weaker argument for long term network security, but since tail subsidy schemes are unable to make a strong argument that they're actually able to meaningful improve security (much less guarantee it!) I don't find that weakness particularly compelling. There are many uncertainties about Bitcoin's security and long term income for mining being insufficient is one of them (probably not even the most concerning one). Making the economic policy clear and simple is worth it, especially since security isn't going to be clear regardless. I'm pretty confident that if Bitcoin originally had perpetual subsidy the market would just be further diluted by variants that had different amounts of it. Zero is a pretty strong attractor in the design space, 0.01 vs 0.02% is far less clear.
I think our experience so far makes a basic case for Bitcoin's security: Bitcoin generates fee income today which is greater than the total (inflation subsidized) income of many altcoins that seem to be going without attack. Is this a security guarantee? No, but it's the first test and Bitcoin appears to be passing it. Assuming it does work I think we're obviously better off with it as it is-- I don't think anyone arguing for tail subsidy would still argue for it if they were confident the system would be secure without it: The only time you can make a clearly moral case for forcing someone to pay someone else is on the basis of necessity. If Bitcoin's scheme turns out to not work out then users in the future will have many alternatives they could consider-- including adopting Bitcoin variants that are created that have constant subsidy (as tail subsidizers propose) or attempt to achieve security through other means. To those people, should that future ever come to exist, the discussion will be much simpler though because they'll know if Satoshi's simple economic-effect minimizing scheme works or not, they'll know if alternatives are
necessary.
The subject just creates drama today because we all clearly signed up for a system with a particular economic policy, for better or worse. It would be immoral in the extreme to try to coerce people onto a different one. And since for the moment Bitcoin does work I think it's hard for some people to see conjecture on this subject as anything but a call for coercion. Fortunately, for the same reason I think it would be impossible to do so, unless it turns out that Bitcoin isn't viable-- and in which case it wouldn't be that big a deal because few would want to stick to a system that wasn't working. If Bitcoin users didn't think a non-cocersive system was extremely valuable they wouldn't be using Bitcoin to begin with. I think Todd's post acknowledges this out too, but people seem quick to ignore that point because they'd rather stress themselves out over the drama (presumably this propensity was also a factor why Todd stopped developing bitcoin many years ago.
).