I got into an argument with someone online over the popularity of marmalade
That seems silly. What kind  of argument over marmalade was it?
We also started to insult each other insensibly, we insulted each other's family and even threatened to kill each other's cats
You can disagree with anyone you want to. However, online arguments get rather silly, do not bother to do that anymore. These arguments are done by trolls and you don't want to end up looking like one of those.
I'm not going to stop since this is so much fun.
You might be having fun but the other person might not. Threatening to harm someone else isn't a joke. They might report you to an admin and get you banned.