Yes, I understand how financial contracts work. But like I said in my original comment[1], at the top of this subthread, that provides vital context for the point I'm making, this was big enough to have the potential to
cascade, i.e. be such a big loss -- against such a formerly-safe capital buffer -- as to spill over to other financial institutions, bankrupt them, then spill over to their counterparties etc, and eventually to the broader markets that are many degrees removed.
The kind of situation they were worrying about and rushed to prevent in 2008, IOW.
You are correct, in a trivial sense, that maybe the entire market should have just not trusted anyone else, except perhaps under extreme constraints, which would have amounted to almost no financial intermediation and thus almost no financial industry whatsoever. But even the most hardcore "you should have vetted your counterparty" finger-waggers aren't willing to go that far.
[1] https://news.ycombinator.com/item?id=33608638