“30 years ago, it was considered a bad thing to be racist in polite society, so racist jokes were less common, so fewer people were offended by them…”
The definition of “polite society” depends or depended on where you were. It’s a big country. Some may have lived in bubbles where they heard less of this, but that doesn’t mean it didn’t exist. Even in liberal areas.
This is a case where maybe you should have specified the groups you meant. And where.
No one can really blame those who take the brunt of this for being offended. That’s a form of shooting the messenger. Or, “I’m not offended, what’s wrong with you?” Sometimes, a little sensitivity is s good thing.