The main problem is that Bitcoin cannot function alongside other fiat currencies without any problems if it should expand in any significant degree. It will necessarily eat away at other currencies "market" by crowding them out of circulation and making these currencies inflate due to that. With such countries and currency zones like the US and EU it may not matter much because of their sheer size, but with small-to-medium countries the effect may be well felt, especially when people start heavily transacting with bitcoins (instead of local fiat)...
And the governments of these countries will be less than happy
By the time Bitcoin grows larger than is the case right now, the importance of fee income for pools is also becoming larger due to the block halvings. With that in mind, it will be less and less interesting to use Bitcoin as currency tool for day to day transactions as
it will cost you more than you'll get in return. Especially when you consider that current fiat related payment platforms are also moving forward, where the cost of using it for people is zero, and all payments are instant. Another plus for these people is that they also enjoy buyers protection. I don't think we'll ever come to a point where even a small or medium country is feeling the impact of people transacting with Bitcoin.
Some folks might not quite
agree with you on that
You implicitly assume that all things will remain the same, apart from the block rewards eventually tapering off, of course. But we can't be certain of that. In fact, we can be quite certain that things won't remain the same. When halvings are essentially over (i.e. block rewards become negligible), the Bitcoin price simply can't exist at its current level since no one would be able to support it. It should go either a way up, with prices hitting the moon, or a way down, with prices hitting the floor. The first case is possible only through wider adoption, but wider adoption is not possible without increasing the Bitcoin capacity to process transactions. But more transactions means more income through fees even if the fee amount remains basically the same, right?