Trump is not Romney or McCain. It's not a left/liberal-only claim that Trump is dangerously unfit to be president. There are scores of republican national security experts who have written open letters, come out publicly against him, etc.
To claim he's just another side of a coin is absurd. This guy is out there, as we speak, dangerously fanning the conspiracy that the election will be rigged.
The decision by YC sent a signal about diversity of opinions. But, it sent other signals as well. One is that it further normalizes Trump. One can make a strong argument that of the signals YC could have sent, the latter is worse.
Where's the line? Would Trump need to literally have been a klan member for it to be okay for an organization to say, you know what, we're not going to associate with people publicly supporting this guy? Somewhere there's a line, and many of us believe it was crossed a long time ago.
The other thing is, Thiel is not going to be 'unfairly silenced' if YC were to cut ties. He's a vocal billionaire who in our current system of money and politics has a megaphone far larger than most. It's disingenuous to equate YC cutting ties with Thiel to firing an employee over their personal political beliefs. It's a privilege to serve on a board at that level, and there should be a higher moral standard.