Fucking creep #2 emerges from the termite pile. If you call someone a "suspected crackpot" while admitting it's "outside your time and expertise", that's unprofessional behavior. It's going outside your professional experience to label a person for being more ambitious than you. EVERY scientist should be trying to solve really hard problems. I'm not a crackpot, and I'm safe to interact with if you treat me with respect like an equal human being. If you're not willing to treat others as equal human beings while pretending not to evaluate them, you aren't safe and you aren't professional, and if you call someone out for defending their career while fretting about the bully, you're just a bad person.
The first response from Matthew is blunt, but not insane. “People are almost certainly assuming you’re a crackpot” is harsh phrasing, but the substance is a real academic social fact.. if someone has a PhilArchive paper claiming a proof of the Riemann hypothesis and is also promoting a unified field theory, many working researchers will assign an extremely strong prior that the work is not serious. That may be unfair in an individual case, but it is not irrational, and it is not necessarily malicious.
The reaction after that is disgusting and a real warning sign. Calling him an idiot, a crackpot, a shithead, accusing sexism without clear evidence, attacking his career, demanding “find the flaw or shut up,” and repeatedly escalating in public is exactly the kind of behavior that makes serious people disengage. Even if the paper were good, that style would make potential reviewers think, “This person is not safe to interact with.”