In all of your example topics (and others), there are clear sets of "acceptable" and "unacceptable" opinions, and if you share an unacceptable one, you face all kinds of potential work-impacting repercussions ranging from "sad faces" to getting fired.

In the spirit of imagining you're in the out group: Imagine you're a Trump supporter and work in a big-name SV tech company. Someone asks you at work "Boy, Trump is a bonehead, isn't he?" Well, now you're put in a no-win situation: You have to either lie about your beliefs to keep everyone happy, share your beliefs and risk getting fired or some other type of discipline. Or, you'll need to dodge by saying "I don't think it's appropriate to talk about politics at work," leaving it to the asker to speculate about your views.

Remember "Invasion of the Body Snatchers?" At the end where most people are aliens and the few real humans have to put on a fake persona in order to walk around freely? If you slipped up and dropped the persona for an instant they'd all point at you and make that alien noise, and you're done for! That must be what it feels like to hold unorthodox political views working in a Silicon Valley tech company these days.