No one is saying punish any classes. The idea is that you can cast normally, but doing so is harmful to the world around you. There’s no penalty for this; no real drawback except the knowledge that you’re contributing to the world being in the state it’s in (but how bad can it be? everyone else does it, what’s one more spell in the grand scheme of things? The world is already too far gone to save anyway...) But if you want to cast responsibly, that’s an option. You can willingly accept a drawback to do your magic carefully enough not to kill the world just a little bit more. It shouldn’t feel good. It should feel like choosing to bike three hours to work when you have a car and can drive there in 30 minutes.