Protesting the speaker's ideas is always fine. Protesting the speaker's existence is difficult to intellectually justify as a healthy exchange of ideas, includ

Protesting the speaker's ideas is always fine. Protesting the speaker's existence is difficult to intellectually justify as a healthy exchange of ideas, including critique. These days, what we see is a lot of the latter -- up to and including attempting to prevent attendance of the event -- and very little of the former.