What are the bounds of toleration in a academic institution? (Sam Clark comments)

In the thread about the Nietzsche club affair, Sam Clark of Lancaster University posted a comment that I think is worthy of discussion:

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Let me disclaim any ambition to adjudicate this particular case, about which I know next to nothing, and focus on the issues of principle that might apply to it.

[Let's call PL the position]  that harm or the threat of harm is a necessary condition of our using power to interfere with speech, discussion, public meeting, political organization, or political recruitment.

I have three objections to PL:

1) PL is politically naive. If you don't interfere until there are blackshirts on the street beating people up, you've probably left it too late.

2) PL assumes a contentious definition of 'harm'. The 'who gets to decide?' question is a problem for everyone, not just for me: in particular, [the defender of PL] is claiming the right to decide (a) that a discussion seriously entertaining the idea that some historically and systematically oppressed kinds of people are inferior and should be subjected to hierarchical authority does not do or threaten harm; and that (b) preventing a group from using institutional capital (meeting rooms, communication networks, attention) to facilitate that discussion is or does.

3) PL takes as settled what should be subject to democratic deliberation: the bounds of toleration.

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Most readers seemed to be squarely in the "PL" camp.   How do they respond to these points?