Of course, there's also the fact that this situation regarding the devils is completely unprecedented.
As far as the novels go, there's only been one precedent of a devil (demonized human) that survived the process and maybe retained enough cognitive function to use magic.
Humanity is facing a new threat, and the only information the normal peeps have is that they're dangerous and a bunch of flying kids can wipe out hoards of them.
Humans are REALLY bad at recognizing and gauging how bad or dangerous something is, and we're worse at dealing with such threats. Our greatest learning device, PAIN, requires us to put ourselves in danger to learn.
Here in real life, we didn't really understand how bad the coronavirus was until it broke quarantines, thousands started to die, and we all got trapped in our own houses.