Silicon Valley people live in a bubble where everyone they know is smart and liberal. After a while they forget that there exist smart people who are not liberal and implicitly think that if someone disagrees with them, they are uneducated and just wrong. Consequently they take it upon themselves to demand that people not be allowed to say incorrect and uneducated opinions (really just anything the Silicon Valley hivemind disagrees with).

When nearly everyone in your bubble has the same beliefs on politics and culture you will react violently towards threatening ideas.