I don't think anyone in the field is triggered by some guy pursuing his interest in aliens and UFO.
What they get triggered about, is that guy using his relatively large platform to say that anyone not agreeing with him is part of the establishment or otherwise useless, or to say that there is no other possible explanation to a certain phenomenon than aliens, or to be insulting to another colleague during an online talk.
When did this happen? In the podcasts and interviews I heard, Loeb was often provocative towards the establishment, but I never saw him make negative comments about an individual.
[1]: https://www.forbes.com/sites/startswithabang/2021/02/16/watc...
[2]: https://twitter.com/whereisyvette/status/1360771406661881857...
If anything, I would say the annoyance is that for the department head of Harvard to be spending his time (and seeking fame) on topics like this, instead of using his position to 1) further "real" research, 2) address problems in the field, 3) in general, make more of the role he has, is something of an insult to people trying all their lives to reach such achievement.
I think it is great that some professionals actually do this, if everyone's a cynic it would just be sad.
I think he's achieved professional recognition, paid his dues playing the game of academia (very successfully), and is now pursuing things that he finds most exciting. The man has co-authored a thousand papers, literally, so I doubt he'd get much marginal excitement from hypothetical paper #1001, i.e., another instance of fitting a curve through noisy data to build support for an obscure model that very few researchers care about.
He has also pointed out that it's an invitation to ridicule in academic circles to talk openly about UFOs. He doesn't care though (why would he?), and that for sure is triggering folks who take themselves very seriously.