Just that, really.
Have noticed this on all forums/groups I am on. Someone will mention a cat/a problem with a neighbour's cat and someone else will 'joke' about killing or injuring it.
No idea why people think this is ok and it doesn't happen to the same extent with dogs. It's fine not to like cats but why in the world would you say, especially to someone who clearly does like cats, that you'd like to see them hurt?
Feel like this constant drip of casual cruelty translates to real life and people being callous towards other people's pets in real life too.