Humans don't "go in heat" to where they have uncontrollable biological urges to find a mate

You must've skipped high school.

The need to mate is one of the primary reasons indoor cats will randomly break out of the house never to be seen again. A spayed/neutered indoor cat is extremely unlikely to do so.

Great! So we agree that it is done, not for the sake of the cat, but for the sake of the human parent who misses the cat.

Humans and cats are both overpopulated. Which population needs more control is irrelevant.

I very much agree that it is irrelevant, until we start taking action towards one but not the other. Then it becomes relevant.

Cats are an invasive species that decimate local wildlife populations

This is an very good and interesting point that I am curious to research more on, it is the only argument that I will concede on: Δ