You are correct. Race, ethnic, gender, sexual orientation jokes can be mean spirited but they usually are just referring to light hearted stereotypical images associated with groups of people and no malice is intended whether they be about black people, white people, Italians, Mexicans, Irish, Scottish, Jewish, redheads, Republicans, Democrats, men, women, Catholics, Jews, Muslims etc. etc. etc. But in our politically correct world, it is only the jokes about black people or Muslim or Jewish people or gay people that are verboten.
And because light hearted humor is only forbidden when it includes black people or Jewish people or Muslim people or Gay people, those groups are singled out or held up as 'different' or 'more fragile in sensitivity' or some such. And it does make it more difficult for the national pysche to then see these groups as mainstream. And if anything, it pushes any prejudices deeper and reinforces the stereotypes. All others can enjoy the light hearted banter about 'hot tempered red headed Irishmen' or 'stingy Scots' or other good natured digs that are okay because everybody knows its all in good fun. Italians 'talk with their hands', the Germans are excessively industrious, etc. If the joke isn't mean spirited, it should be okay. "Dumb Polack" is mean spirited and is offensive to me, but it isn't considered off limits in the PC world, at least to the extent a joke about a black person or gay person would be. But it can be used for good effect when the 'dumb Polack' turns out to be not so dumb.
In the current dynamic, we all recently heard about a fireman who was censured for bringing a watermelon to the firehouse on which a number of black firemen were assigned or circumstances in which fried chicken would not be appropriate for the same reason. How stupid is that when most of us who are not black enjoy watermelon and fried chicken? When 'sensitivity' is carried to that level it only heightens resentments and introduces toxic elements that are entirely unnecessary and help keep racism alive and well.