c'mon guys, why the hell you take it that serious?
Tell a joke about gays.
Tell a joke about lesbians.
Tell a joke about single moms, preferably with a few kids, each of different race.
Tell a joke about a woman's body in the office.
Tell a joke about blacks in public.
Tell a joke about handicapped persons.
Tell a joke about a Jew i Auschwitz.
In the US any of those would be treated very seriously, they could easily lead to lawsuits, and if you're in any position of substance your career would be pretty much over. They'd rip you apart.
Jokes often have a purpose other than just humor. They can be, and have been a powerful political tool to shape public opinion in support of wretched policies.
When you consider that someone suffered unfairly you'll be likely to feel sympathy to them. But if they are stupid then their suffering acquires a comical tone, and therefore is perceived as irrelevant. What comes to the fore that they are stupid and funny, not that they suffer.
That's how the English got away with abusing generations of the Irish "drunks".