An Ignorance Bonus

[Compliant]

I remember hearing this concept somewhere (I can't remember where exactly) that basically gave you a huge bonus against anything magical but you are forced to never associate with magic again.

Basically you have a character with really low Int who doesn't believe in magic:
-they can't be buffed/healed by magic
-magical items become mundane in their hands
-magical attacks glance off or dissolve away when they make contact
-when a magic user comes in contact they can no longer cast

Does a concept like this already exist? If it doesn't would it be broken?

In the end it would be a character who is a walking anti-magic field

[ComaVision]

Maybe the Forsaker prestige class? They get a lot of bonuses to make up for having no magic but honestly it falls short.

[Urpriest]

The problem is, something like an antimagic field only goes so far. It doesn't protect you against things created by magic (Golems, corporeal Undead, Owlbears), or things hurled at you with magic from outside its reach. With just AMF-like protections, it would be hard to impossible for a character to avoid believing in magic.

If you try to avoid that, and allow protection from indirect effects of magic too, then you run into the problem that everything in D&D is an indirect effect of magic. Souls have magical power. Anyone who was Resurrected is only walking around because of an effect of a spell. The PC races themselves were likely created by some divine equivalent of the Origin of Species spell. And so forth. A PC who was totally unaffected by magic would just play in a different campaign from everyone else.