You don't need to teach them in the classroom, but they are an important part of understanding a language. Most people will learn them from their new friends (outside of the classroom), and that is probably the best way.

I have a personal theory that most people (particularly younger men), once they found out someone they have just met is not a native speaker of their own language, will find a way to ask how to swear. It is probably the main thing they want to learn. I have no issues with people wanting to learn them, or if the teacher is comfortable enough to do so, to teach them. There is, of course, a time and a place for such language, in being an adult is knowing this. I don't mind knowing the words, since it will teach me when someone is being rude, or calling me names, or generally being unpleasant.

Personally, I believe that adults should learn swear words as they master the language. You don't have to use them but how can you understand the essence of a language if you don't experience it in its totality? Swear words exist for a reason. Better yet, they can be windows into what the cultural values exist within the language itself.

Completely agree

I think it important, because knowing all aspects of a language is important. They can even be taught in the classroom if done professionally. If a teacher is uncomfortable with this, they should say so. In many languages, profanity is a common part of informal conversation and can be particularly important for emotional nuance in conversation.