It's generally a tone and context thing. Also every bit I have ever done was to communicate a sincere belief whether by just stating it with a joke or mockingly claiming a belief I disagree with.

Jokes are based on assumptions and carry semantic payloads. It being a joke doesn't mean they don't mean it and that it is above criticism for what it's saying. People generally do understand this but often pretend not to to make a point

take as an example bullying if I made a joke about someone being a worthless idiot I would be actually calling them an idiot and using a joke to do so. Or if someone joked about Jewish people being greedy that would be actual antisemitism that coincidentally takes the form of a joke