Assuming that everything has been done to eliminate the possibility of injury/physical discomfort:
I think that yes, moving a horse like this is possible - and not irresponsible, if you do it right. It seems as if you’re completely open about what his behavior is so that’s already in your favor. It’s clear that you want to set this horse up for success with someone else (and set that person up for success as well).
I’m an amateur rider. My horse, who recently passed, was not amateur friendly. For another rider, he was easily a dangerous horse to ride. For me (and my trainer) we knew what was coming, how to anticipate it, and could ride through it. Likewise, my trainer’s horse is savagely unforgiving of an amateur ride (and he sounds more in line with your guy). I can ride him without too much of an issue because of my extensive familiarity with his behavior and my experience with riding through things with this horse before.
“Is this horse dangerous?” - you identify the caveat that all horses are dangerous. Great place to start. At that point, it’s all about risk assessment. There are some amateurs who have grown up with hard rides. For them, the horses they ride aren’t necessarily more dangerous because they have the education and experience to manage it. For another amateur without that degree of feel, awareness, or experience, the horse might be more dangerous. “How dangerous is this horse?” is always a question whose answer I think really is dictated by “How good is the rider?”
Ultimately: I would look at an experienced amateur who maybe wants to look at being more competitive - and one who works very closely with a trainer. Insist on trial rides (both the prospective new home AND their trainer) to make sure all parties are comfortable with the situation. If possible, replicate the situations that your horse reacts most strongly to so they can see what it is (and maybe with the trainer on, so the trainer can assess if this is viable for their client).
I don’t necessarily think you’re dead in the water with rehoming this horse - but I do think there’s steps you should take to ensure everyone’s all on the same page with what the problems are, and completely comfortable with managing them.