You're meant to buy(sell) because you like the idea of (not) owning something. That means you don't want to move the price. If you move the price you can't buy more at the same great price later. Wanting to move the price is sort of the smoking gun of manipulation.
Being able to change the price in the short term means the price is "wrong". A wrong price cheats all sorts of market participants even ones who don't trade.
Securities fraud is defined as any action that "induces investors to make purchase or sale decisions on the basis of false information"[0]. A false price is a great false piece of info to manufacture.
I'm watching with interest for when WSB attracts the interest of the regulators. Being retail means they're generally ignored, until they're not.