Protesting against a view is not the same as shutting down a lecture. That is as much an expression of free speech as the lecture is. The protesters cannot shut down a lecture. Only the university can do that . If the people in charge of a university have no desire to shut down a lecture, no amount of protesting would force it to do so. I can only assume that, at least in some of these incidents if not all of them, the people in charge of the universities that shut down lectures do so because they are willing to shut down speech they personally disapprove of and are using the possibility of violence from protesters as an excuse to do what they want to do. Even as along ago as when I was in college, there were professors that were unwilling to engage in debate and insisted that their position on an issue was the only possible one to hold. I am told that this has become more prevalent in recent years and that a sort of orthodoxy of thought was encouraged and dissent from that orthodoxy was not only discouraged but might even be retaliated against. I know this last is hearsay evidence as I have not attended a college class since the early 90s, but my experience then seems to indicate that this may well be , to some degree, the case as it was then even more likely that a professor would be intolerant of dissenting opinions than it had been in the 70s when I was doing undergraduate work. If those same intolerant professors I knew in the past gained authority in the university I would assume they would run the university in the same intolerant manner they ran their classes.