Seems to me that the people who get accepted by YC (and, most likely, the majority of the people who apply to YC) are the kind of people who would be doing thei

Seems to me that the people who get accepted by YC (and, most likely, the majority of the people who apply to YC) are the kind of people who would be doing their stuff with or without the help of YC. As to a bubble - without getting into that debate now, even if it later turns out that we're in a massive bubble right now, YC are investing money/time with the purpose of making money, so they're in the same situation as the founders themselves, in that they don't want the bubble to burst, and they don't want to see their startups fail.