Outdoor cats are bad because they devastate native bird populations vs but just look at him, kitty wants to go outside, you are the oppressor!
But it became a massive multi-thread argument, that spilled over into jokes about how dumb this is that it got so heated, which usually ended up with more of those arguments in them.
I think this was back with the old Active algorithm that basically prioritized flame wars, too.
This was the first time it happened with something that wasn't, like, war and politics, so it became a meme.