This is not a pump and dump. In PnD, there is an element of subterfuge - the people you are selling to are unaware of what is going on. In this play, all actors are fully informed of what is going on. I mean, maybe some people don't really understand the details, but the majority of people here aren't buying GME because they think it'll keep going up; they all
know it's overvalued, but they don't care, because the goal is only partially to make a profit. 'Pump and dump' isn't illegal per se, what is illegal is lying about fundamentals or circumstances to influence stock price. That is not what is happening here.
Furthermore, if you're arguing that it's illegal because it's done in group, then I don't understand what legal basis you are using for that. I also don't understand why you'd say it's "very different" from doing it on your own. I can't think of anything else off the top of my head that legal to do on your own, but illegal in group (some things are more illegal in a group, but that's not what we're talking about)