This is the entire ethical basis of animal testing, except in this case, they’re at risk of actually helping the animals they’re testing.

Compare that to e.g. malaria trials where they buy mice, infect them with malaria, and then see if the malaria responds.

I’m a vegetarian because once I made the leap that animals probably have an internal experience, torturing and slaughtering them so my mouth can feel a certain way strikes me as not personally justifiable. How much worse is that? Should I go around calling everyone a monster? Hardly.

Animal testing at least has some meaningful rationale, and testing treatments for diseases animals actually have seems solidly in the realm of ethically justifiable

I don't want to sound callous, but... they're cats. Not humans. How do you think all the medicines at your vet's office were originally tested?

Animal models are used in biomedical research all the time, and yet they account for a tiny fraction of the animals we kill for arguably less useful purposes (meat production). Provided steps are taken to minimize any unnecessary suffering (which should be relatively minimal in a drug trial), I find conducting research on animal models far more justifiable than even just eating meat - there's an alternative to the latter (vegetarianism), there aren't good alternatives to the former.