No-coiners are not losing their purchasing power because there's none unless and until you liquidate your stash.
That's if you view Bitcoin as a commodity that needs to be liquidated (ie. exchanged into a fiat currency) before using it to spend on goods and services. Since you can use Bitcoin as a currency this line of thinking doesn't fully apply in my opinion. Of course one may argue that someone somewhere down the line will have to exchange Bitcoin into their local fiat currency but then again this applies to international trade with foreign currencies as well.
Okay, you bought your bitcoins cheap and sold them dear, so your purchasing power did in fact rise. However, it rose thanks to someone buying from you and not because of someone who doesn't or didn't have any coins, to begin with.
The (relative) rise of purchasing power is twofold: First, due to the rise in price of course. Second, however, because the rise of wealth in a group of people often leads to goods and services becoming more expensive for those outside this group. Most commonly you'll see this when cities or city districts go through a process of gentrification -- In absolute terms the purchasing power of the disadvantaged group might be unchanged but in relative terms they are pushed down. In a way you could see this as realized opportunity cost.
Now the severity of this secondary effect is of course debatable and will largely depend on each individual situation (ie. how strong your local currency and how wealthy your country is). And its impact is likely limited unless Bitcoin pulls a McAfee for whatever inconceivable reason. However I would not completely dismiss its significance.
Similarly, you can't say that no-coiners are betting against Bitcoin for the simple reason they are not betting at all, either in favor or against it
Depends on whether you want to account for opportunity cost.
As with most things it's a spectrum, with no-coiners being straight in the center, but some lines of thinking necessitate a binary cut (ie. "if you're not with us, you're against us"). Upon inspection this may be a sign of being on the wrong track though.
For example, miners are not buying any bitcoins but they are still selling them. I see you are going to claim that they effectively buy bitcoins by paying for their mining rigs, rent, electricity, whatever, but that would be a faulty logic anyway, even if we accepted this assumption. How come? Because their "purchases" don't contribute to the price growth as they don't "buy" these bitcoins in the open market. Then, you could just assume that by selling their rewards they are in fact betting against Bitcoin, which is the case in real life as their sells do indeed move the price down. It is hard to get around this
Excellent, excellent point. I'd argue that whether their "purchases" contribute to the price growth depends on whether they are holding or instantly selling to cover running costs and then some.
If they hold, they contribute to price growth in that they are literally withholding supply from the open market (and from other miners that instantly sell). I do concur that the majority of miners is likely "betting against Bitcoin", however it'd still be interesting to see what percentage of coins get immediately sold vs held.