I think it's a very slippery slope to base endorsement on a person's political actions. It raises some important questions:
-Do you stop endorsing and associating with everyone who supports Trump? Where do you draw the line logically?
-Why can't people with opposing views work together and agree to disagree on the elections and let the votes speak?
-I imagine Trump haters and Hillary haters have very strong reasons,facts,opinions and speculative thinking to backup their claims that the other candidate is a threat to democracy, will start WW3, corrupt practices etc. This should lead to well informed debate as it seems to be happening here but without calling for distancing from person X for endorsing a different candidate. What will you achieve by distancing people based on differing views? A monoculture? Differing views and discussion on the views is one of the things that makes a democracy work.
I believe Sam is right on this. It's Thiel's money, he can support whichever candidate he wants (it's legal). His views differ from Sam's and PG's, and people seem to extend it to YC as an organization and call for distancing Thiel from YC. It achieves nothing, and if anything weakens democracy.