Neither really. Sort of.

There are certainly inherently repugnant beliefs, but beliefs in and of themselves are harmless - they’re just a particular pattern of firing neurons in a brain. They literally cannot bring harm to others just in and of themselves.

The thing that makes some beliefs horrible is not the mere holding of them, but the things one who holds them is likely to do. It’s those acts that are the real evil - the beliefs are just a foundation, or a trigger.

Now, all that said, I would hazard that it’s exceedingly rare at best (and arguably impossible) for anyone to hold noxious beliefs without them in some way affecting their behavior, so the mere holding of noxious beliefs can certainly serve as a justification for the conclusion that the person in question is in fact horrible. Still though, to be (perhaps overly) precise, I’d say that it’s not the belief itself that makes them a horrible person, but merely that the belief makes it quite likely that they’ll act in ways that make them (or reveal them to be) horrible people.