About curse words being offensive to Christians, neither God nor the bible dictates which words are curse words and which aren’t. People/society did. So if people/society decide they aren’t offensive anymore, why would they still be a sin?
Simply by virtue of their being offensive and often vulgar or blasphemous. They aren’t intrinsically wrong, and there’s certainly nothing wrong about having a conversation like this. There’s nothing immoral about listening to music with swear words in it, as a priest assured me once. However, it says in one of St. Paul’s letters, “Never let evil talk pass your lips; say only the good things men need to hear.” Swearing, slander, gossip, unkind criticism, verbal abuse, etc. all fall under this category. I don’t think anyone would argue that swears are good, nor would they disagree that many find them offensive.
All that being said, I don’t think swearing is a very serious sin (and isn’t always a sin), unless it is done with the intention of offending or angering someone.
Also worthy of consideration is the fact that swears are often used when angry, and are thus associated with anger, and that swears in a number of languages are also blasphemous; i.e. they are religious words used in a disrespectful way.