For the same reason that there should be jokes about pretty much everything. They're a form of human communication and expression which can be very valuable to group dynamics.

It is perfectly possible to joke about horrific things without intending to condone or support those things. That said, the place for these jokes is unlikely to be in groups of people you don't know at tech conferences. That's insensitive, rude and often intimidating - so don't.

Because we like laughing. Women laugh about men, men about women.

because purposely offensive jokes can be funny in the right context and when you know the jokester doesn't really believe in what they're saying

You shouldn't eat tomatoes because I don't like them.

because they're funny

Yep, all the jokes should be censored for fear of causing offence.

Because.