That's the "default" way of thinking among Bitcoiners, and I respect that. But I'm truly curious if more and more people believe that removing the supply cap would be a good idea as well since Peter Todd mentioned that it's more sustainable for the network to have some sort of inflation of supply to support miners.
I do not believe the number of people who believe removing the supply cap would be a good idea is increasing. If we ever get close to a necessity of that happening, we would probably get as close to it as we can when the price of Bitcoin does not offer significant increases every Halving any more and Miners are starting to feel their operations as a burdern and an expense rather than an investment with returns.
And I do not know if it will even happen at all considering the higher the price Bitcoin has, the more monetary return they will get from Fees while the Block Reward decreases. It is thought thorough enough even for the 2140 situation because while the price of Bitcoin and usage increases and the Block Reward decreases, Fees we consider small today will be worth a lot more by then. Enough for their Mining operation to STILL be worth it.
Now say you are right and Mining will soon not be sustainable any more. If we ever get there, I presume it may happen about five to ten Halvings from now at the very earliest when Miners may start to seriously feel a decrease on their Block Reward returns. Because if one thing is for sure, it is that Bitcoin can not sustain incredible price gains every Halving and at some point it will probably only double on average every Cycle. And still. As usage increases, it will offer enough incentive through Fees in my opinion. But I will continue your scenario.
If you ask your self what happens if Bitcoin ends up not being used that much any more. The way I see it, I do not know if Satoshi thought about this aspect but it kind of looks like it. Because,
-If Bitcoin is not used enough by 2140 for Fees to sustain it then it means its purpose has not been fulfilled. It would be an empty street.
-If the hash rate drops significantly in a short time as in most Miners abandon the chain, the Bitcoin chain ends up stagnating and could stagnate to a point where it is effectively stuck.
I can kind of see these two above as 'kill switches' for Bitcoin. As in. If Bitcoin ends up abandoned and not used, the incentives drop, the chain stagnates, it is like a 'pause' button for Bitcoin. Was it planned by Satoshi? I do not know. But it does make me curious to be honest.
Anyway. I have yet to see Miners complaining about their profitability or even about the sustainability of Mining in the conditions of constantly dropping Block Rewards and a fixed supply. If there is a time where people are going to be ready for discussions around the supply cap, I imagine that would be the time. Or maybe I missed such complaints, although I doubt it?