That is thus all solely your interpretation. I think it is very dangerous to make assumptions about people's internal worldview and judging people on that assumption. In fact I think you have just expressed quite well what I object against, precisely.

Is it ever appropriate to model another human's internal processes?

Imo we do this all the time :) But, perhaps it is important to recognize that those models are simplifications. It's easy, probably tempting, to project a group of humans onto one axis. But it's wrong, you don't know someone until you know someone. A good rule to live by (and imo a correct assumption) is that, by far, most people are kind.

You say most. If someone consistently acts in ways that are not compatible with kindness, but are compatible with bloodthirstiness, may we model them as bloodthirsty?

I'm ok with that for sure. But how many people are we talking?