Both the Arch Heart and the Tree of Atrophy have suggested that Predathos is not actively hostile to mortals, and people that are in favour of releasing it have taken this to mean that there will be no consequence for doing so.
Y'all realise Predathos is a cosmic horror monster, right?
Like, it is most likely an Elder Evil, which is one of D&D's categories of "Things we copied from Lovecraft," and a consistent theme of cosmic horror is that the monsters are very frequently so powerful and so vast that humanity doesn't even register to them. They are the living embodiments of an uncaring universe that can and will snuff us out in an instant, without malice or intent, because they are simply so much bigger than us.
The most powerful entity in the Cthulhu Mythos (Which TSR literally stole from in early D&D editions, Cthulhu was straight-up in early sourcebooks and they got C&D'd for it, the Far Realm-associated stuff in this game has always been rooted in Lovecraft) is Azathoth.
Azathoth is described in his final major appearance as the "blind idiot god", he's a twitching amorphous mass that sits in the chaos outside reality, constantly lulled to sleep by horrible flutes and pipes played by his servants, and if he ever woke up then all of reality would end. Not because Azathoth is malicious, because he isn't. Azathoth is completely mindless, it has no higher consciousness, it's just a writhing lump of eldritch flesh.
There are actively malicious entities in the Cthulhu Mythos, of course there are, but many of them are not that.
We've seen that even communing with Predathos can have catastrophic effects. It destroyed an Exandrian City and every Ruidian surface settlement. There's no guarantee that releasing it won't make a whole world of Molaesmyrs.
Predathos doesn't have to be malicious, it's powerful enough to end civilisation with its morning stretch.