"Those concepts are inherently fuzzy and related in messy ways."
No, they're really not. The one has a strict legal definition and is enshrined in law, and the others don't and aren't.
"But in actuality, de-platforming as practiced on college campuses often results in a group of people too intimidated to talk and too intimidated to attend, contrary to their desires. "
And what about the people who have felt intimidated by the hate speech and haven't attended because of that?
"If "de-platforming" has the effect of censorship, then it might as well be censorship."
But it isn't censorship. That person can speak their views outside of that building. They are only prohibited from having a platform to spread their views. They can still publish a book of them and market it. Nobody has lost any of their rights, unless you're stating that you automatically have a right to enter any building and preach your views. Nobody would get upset if $person was denied entrance to a funeral home for preaching their views there, because we all understand that that is inappropriate behaviour.
A church can expell a person for preaching atheistic views, and nobody gets annoyed. But as soon as someone does it for a white supremacist, a nazi, andor a person preaching for the extermination of certain groups, it's suddenly "against their free speech".
Or, for an even better example, think of twitter as a publishing company. If I go to twitter with a book (tweet), they are not legally obliged to publish it. The fact that they do not wish to publish it, or that they stop publishing it (removal of the tweet), is not an infringement of my free speech. I can start my own publishing company (with pretty much every website host), or go to another publishing company (like /pol/) to have my ideas heard. In addition, people writing to the publisher and stating that my book (tweet) should not be published, because of the views that are held in my book (tweet), that is also not an infringement of my free speech.
If the government decides that what I say is unseemly, and they purge it from all forms of media, from libraries, etc. and state that my views are not to be published, then that is censorship.
[An orthogonal point here is that people like yourself often argue that these people should not be able to write protests to the publisher (twitter). As per your own definition, wouldn't that count as infringement of their free speech? It's interesting how you readily support that views should not be removed, but condone that people should not be allowed to protest against views, or that people should not be allowed to write their point of views in emails and posts about twitter. Surely the right to advocate what you call 'censorship', falls under what you call 'free speech'?]