The problem with so many of the rationalizations I see are all based on tiny, limited scopes and the fundamental change of everything that is Bitcoin.
Segwit + 2MB + LN = all problems are fixed and the world is a happy, shiny new place where growth will no longer occur.
Not!
What if the current masses don't want their transfers "off-chain"?
Then they don't use it. In fact, "off-chain" is a perfect way to connect to exchanges. LN is perfect with exchanges as central hubs, and exchange customers having their holdings in a channel with their exchange, which protects them from theft, and renders the exchanges trustless. It would turn the current exchanges in the new banks.
It most probably won't, unless, of course, in the "exchanges as new banks" world ; bitcoin's main application is "greater fool game", and of course, we need a lot of greater fools, but on the other hand, I don't know how many of them will be gullible - though there's hope, given historical records of frenzy. When "average Joe" gets into bitcoin, sell everything !
Actually, it may be simpler to get "new masses" to bitcoin by giving them a central authority (their exchange) and giving them classical banking with off-chain linking to their exchange. It would be more secure too for them, they would feel much less at a loss, it would be standard banking. There may even be a law that only off-chain transactions are officially allowed, and that you need a licence for on chain transactions.
What if we say, "Core devs we accept no half-way measures, any fork must be future-forward looking"?
Bitcoin is broken beyond repair. The first thing to fix in bitcoin, is the emission curve. A decreasing coin emission renders every coin unstable and/or centralized. The second thing to fix is proof of work consensus. These are the two principal value propositions of bitcoin, and they render bitcoin unfixable if you don't modify them - which goes against bitcoin's belief system.
Only a temporary fix, that is changed regularly, can keep it afloat for a while, and this might very well be sufficient, because bitcoin doesn't maybe need to scale to very very large sizes.
Sure, but the LN could transform bitcoin into classical "banking" (but rather, classical clearing house transfers). Bitcoin is not money, but is a speculative betting asset, and that betting is mainly done on clearing houses (exchanges). Now, the number of players may become large, but has nothing to do with the size of payment networks. Bitcoin being more like "complex derivatives for the people", the LN could be a way to tie yourself to your clearing house and render the relationship more trustless.