Devil's advocate: humans cause an excess of death beyond that of cats: is it better to put humans down to prevent them from causing mass death?

Maybe, though at least humans can make an effort to minimize their harm, and some can actually do good. Cats can't really do this.

I'm not disagreeing that they cause harm, but its a philosophical argument of utilitarianism that deaths of a subset would be better no matter what, right? It's a nuance that can't necessarily be put to black and white contexts. That's all I wanted to put forward, but I may have messed up my argument trying to distill to a sentence or two.

Sure, but again things are dying either way. More things are dying with the cats living outdoors. What makes a cat more valuable than a bird, or tens of bird, or hundreds of birds (or mice, or whatever else)?

The only moral framework that I could think would justify this is hedonism, if the cats bring them happiness and that's all that matters.