Any healthy, long-term viable society has to prioritize one task above all others... making the replacement people that will be society once the current people die. Your society (if you choose to claim it) doesn't do this. Sub-replacement fertility. It's dying because of this. If you think that's fine, go for it.
>I live among millions of people every day
Sure. And each generation is about half the size of the previous. It will look fine, even crowded for awhile yet.
>I understand you're coming from a very American-specific point of view,
This is global. China has sub-replacement fertility. Korea and Japan have sub-replacement fertility. Europe has it, South America has it, India may have finally crept below replacement, but if it hasn't yet it will next year or the year after. This is everywhere. There's not a hidden corner of the world where it's not happening.