This is worrying indeed because the negative reviews are clearly justified.
One thing to consider: if they've provided leveraged finance to buy this stock then they're exposed by this massive move too. They therefore have to manage risk, and so limiting further exposure does make sense. If these people can't pay their bills (if leveraged), I don't know who takes on that risk. It might be RH or this could be passed on to others. Either way someone needs to take that risk on. Some have asked why not just stop the leveraged finance, and I don't know the answer.
Another thing to consider: is it legal to allow manipulation of prices? The folk are trying to hold the price up. This is a tricky subject to consider. As a professional there are various rules on what is manipulation. Presumably a broker has some responsibility here.
All in all, who knows if this is clearly justified. Folk are equally able to go and place orders via other brokers. Whining that broker X can't trade Y doesn't hold water as an argument. If they don't trade X, find a different broker (this is entirely standard practice. Not every broker can trade every instrument). You're not required to execute there.
I'm afraid that folk are going to have a really bad wake up call. These markets are really complex and the warnings that your capital is at risk is a really big warning to be heeded. Don't invest what you can't afford to lose. I'm sorry that people are losing here. :(