When you actually ask these students if they ever experienced hostility from an instructor they invariably say they have not. To a not insignificant degree much of this is driven by the conservative media landscape making conservative students feel that universities are hostile to them, rather than actual personal experience with hostility.
And even more so a lot of the student self-censorship comes not from professor influence, but bog standard peer influence. And it isn't so much as hostility to conservative ideas as much as it is out-group self censorship across the political spectrum depending on the issue.
Not to say that there isn't any ideological hostility on college campuses, but broadening this topic gets pretty nebulous fast and makes it so you quickly lose sight of what are the actual issues to address.