Would you say nothing and hope nobody else notices? Good luck with that. That just means your companies get screwed.
What if you get away with being silent, nobody else noticed, and the bank gets bigger and fails even more spectacularly later in the year? Wouldn't that be worse? Wouldn't you then be criticized for not speaking up when you knew about the problem?
Would you try to band together with other investors to save the bank? Worth a try, but that means you have to tell other people there is a problem and trust that not a single one of them would start a bank run.
A lot of people have an axe to grind against Peter Thiel but in this case he did the only rational thing. If he had done anything else he would have been blamed too, because some people just don't like him. I haven't seen anyone demonstrate a reasonable alternative for how a rational person would act, knowing what he knew at the time.