I'd be interested to know if the university is doing anything about this.
They will probably argue that the students have a right to protest, but if they are bullying and harassing attendees and suppressing other people's free speech, then this crosses a line and the university should take action. The problem is that students engage in this type of behaviour with impunity because they don't expect consequences (and then they carry this attitude into the workplace when they graduate).
I wonder if Michael can do the lectures online? He shouldn't have to of course, but people who want to hear him talk shouldn't be deprived of the opportunity. And perhaps more will attend online where they don't have to run the gauntlet of deranged activists.