It is not that professional traders believe those tweets. A tweet like this is seen as an opportunity to profit from irrational market reaction. It is self fulfilling though. They believe others will drive the price down, so they act upon that prediction driving the price down.
Yes - it is not too far removed from people giving up their private keys in Discord - greed drives behavior and this preys on greed. But, no one seems to be questioning this side of the coin.
You know what it is like from a code perspective - trusting people to do the right thing, is never going to keep a blockchain secure.