David Duke is running for senate. Does that make Holocaust-denial a political issue?
There was a time when women having the right to vote was a political issue. Today it is not (though Thiel has raised concerns about what women's suffrage did for capitalist democracy[0].)
There was a time when slavery was considered a political issue. Today it is not.
I don't think sexual assault is in the realm of "personal politics". I don't think racism is either. Can I take the time to understand people who might advocate for these? Sure, but that doesn't mean I want them as leaders.
Having Thiel as a partner in YC, when Silicon Valley has tremendous issues with diversity already, sends a strong message. It's not about supporting a political party. I'm sure the YC partners have a wide spectrum of political views. This isn't about politics.
[0]: https://www.cato-unbound.org/2009/04/13/peter-thiel/educatio...