I have no desire to live in a 250 s.f. unit. What does my future look like? How would I raise kids, if I wanted to have them? I don't know how anyone outside of the top 3-5% pulls it off in San Francisco.
And to your main question - if you are somehow blessed with the opportunity to make a buttload of money and live on the (relative)cheap for a little while in SF, then your future is probably looking pretty good. We are fortunate to live in a country where you can go wherever the heck you want at any point that you want, especially if you're financially able to do so.
But you need to understand that many of us (myself included) really don't want to have children ourselves.
We are people, too... and saying that all housing needs to be built large enough to accommodate a family with children is unfair and a waste.
I mean, sure, I pay more taxes than someone of my own income with children... and I think that's fine. If the additional taxes were spent on things like education, I'd even be okay increasing that difference and paying even more, but it does nobody any good to say I can't buy a smaller place because you want to have a kid.
Honestly I’m not sure what changed in my opinion. I’m generally very pro-building, but I realize different people want different things.