Idk if admins need to manually approve registration applications for Mbin. Many smaller Lemmy instances are set up that way, so it may also be the case for Mbin.
Regardless, whether the registration is reviewed manually or automatically, the admin is the one who will be able to help you.
Suggesting that we move towards space-based astronomy doesn’t mean he’s out of his mind. He might not be a professional astronomer or astrophysicist, but that hardly indicates insanity.
They had an opinion and expressed it. You can then reply and explain why you disagree. No need to call them insane for expressing their thoughts.