That's a curious position to have on a website focused on entrepreneurship.
Pretty much every YC company risks money (vasts quantities for some) in the hope of making money.
The difference is they are risking other people's money.
Not really. The opportunity cost relative to whatever else the founders could be doing is substantial (especially compared to the typical YC investment they get).
Amazon has a long history of sacrificing short-term profit in favour of long-term infrastructure development, though.
Moreover, no one is seriously questioning the long-term stability of Amazon or its revenue model. A stark contrast with the situation Facebook finds itself in.
Because they had an awful quarter from an EPS perspective. Their revenue growth increased. I'm not sure what point you're trying to make with this.