I'm giving you all an opportunity to rip me and my family to shreds here. Please withhold judgment until you read the entire post. Let me give a recent example from my son.
He works at a major corporation as a blue-collar worker. He is the only white man on his team. The other day he told them,
"Yeah, my grandpa knew Rosa Parks, helped her quite a bit."
"Really, how?"
"He told her, 'Get to the back of the bus'."
Now, hold on for a second. This joke is entirely situation dependent. It is either a funny self-deprecating joke, or a threat. But, notice something, it ceases to be funny precisely to the extent that it is racist. If my son were actually a racist, his co-workers would not find this funny at all. If, on the other hand, my son is making fun of our racist ancestors, then it is a good joke. His co-workers thought it was hilarious.
There is no question that this joke is politically incorrect. Sensitivity training would tell him to never say anything like this. But he has a better feel for what brings the team together than the risk-averse lawyers every could.
Someone from a liberal cocoon might be horrified at this example. I'm not at my son's work, but since the team is a bunch of testosterone-drenched males in a physically challenging environment, I can imagine that they have nose-to-nose confrontations and I wouldn't be shocked if there were occasionally some pushing and shoving. This is a 'normal' workplace and someone complaining about it should "get a life."
As an opposite example, I mentioned the crop-dusting place. Most of the employees were illegal aliens and they were used and abused. At that place, anyone who shared an accent or coloring associated with them was not promoted. The place was run by a rich family of Portuguese descent and they did not like Mexicans. Any racist "jokes" that were told there were entirely truly meant and intended to keep the Mexicans in their place.