How do you figure that? You stated,
Trump is an incoherent, babbling moron. Why would a university invite him to speak? You start off by insulting Trump and his ability to speak. Clearly, what you stated is hyperbole in that respect at best. You might not like what he has to say (and I don't have to either), but you use that as an excuse to say he shouldn't be invited to speak at all.
Why would a university ask him to speak? Because, like it or not, he is a major public figure right now. Diversity of ideas and hearing ones that are opposed to what you, yourself, might hold is the whole basis for free speech and exchange of ideas. A university is supposedly the premier location that should be happening. But as I pointed out, a Left leaning to Leftist university wouldn't invite someone from the Right, Trump being only an example. There is a long list of Rightist / Conservative speakers that have been "disinvited" (eg., banned) from speaking at universities.
https://www.thefire.org/how-to-use-the-disinvitation-database/
The Left eagerly justifies this as reasonable.
https://www.vox.com/the-big-idea/20...ndment-college-campuses-milo-spencer-protests
https://newrepublic.com/article/142218/colleges-right-reject-hateful-speakers-like-ann-coulter
The reason Rightist speakers are rejected, when you get down to the details, isn't because they are "hateful" or "fascist" but rather because those at Leftist universities
hate and oppose all dissent and differing opinions. They simply don't want to have to listen to someone who says things they don't like.