Blanket IP banning is lazy
Blanket IP banning is easy and indeed it is safe because if people cannot access your service then they can do no harm to it. The blanket ban approach may work well for some local sites but if that is not your case then it will work against you.
Blanket IP banning worked well 10 years ago but not anymore, things have changed, a lot, these days you'll find malicious bots sharing IP addresses with legitimate users and unless your case is very specific I'm sure you don't want to ban those legitimate users.
Blanket IP banning is bad, laziness is bad.