You make a valid point that having a lot of whales is a double edged sword. They can provide a lot of demand, but if they lose interest and leave, they can equally remove a lot of demand very quickly (as you say causing a crash). So there is definitely risk there. On the other hand, there is no guarantee they will leave, and doing so would likely cause them large losses, so the crash you describe may not ever happen, but it is certainly possible.
BTW sell walls away from the market usually means someone wants to buy.