Trump is uniquely dangerous and I would fully endorse YC cutting ties with prominent supporters/backers of his...if that would do anything concrete to reduce Trump's chances of winning the presidency, by even one epsilon. I don't Thiel doing office hours for YC companies gives him any sort of tactical advantage he could parlay into assisting Donald Trump's campaign, though I'm willing to entertain arguments otherwise…
But why only prominent? And if not where does this go? Do you now ask anyone who does business in any way shape or form (vendors, employees, YC applicants, the cleaning crew etc.) what their political or personal views are and then cut ties with them as a result? Or is the line arbitrary "we know it when we see it". Kind of like a boycott?