So I've been browsing okcupid again and in some girl's profile I read "do not message me if you think rape jokes are funny". That's interesting, I thought. Because, honestly, I don't have any specific opinion about rape jokes. Maybe some of them are. But, if you ever try to tell a rape joke to a victim you're probably be the biggest asshole in the world, even if it is indeed hilarious. So it seems that the degree of fun of the joke doesn't matter at all. My assumption would always be that many jokes may potentially hurt someone. Sometimes you can easily tell if it would hurt the person - like some of the race jokes, for instance. In other cases, as in religion or profession jokes, it may be harder to guess. And so, the harder it is to determine whether a joke is appropriate, the more cautious you would have to be.
Truth is, people who say that racist or rape jokes are totally okay just don't feel insecure about being subjects of those jokes. However, every person has something to feel insecure about. Once you make a joke about it, even if it's perfectly acceptable by the community morals, you're crossing the line. And that is what should be taught to people, not that some sorts of jokes are a taboo and others are not.