Swear words are bad because people continue to think them bad. Your choice to use them means you have no regard for others who are offended by them. That's fine, but it says something about you as a person -- that you don't care about many of those around you and don't respect them or their beliefs. Again, you may not believe this is true, but I can point to scores of people that do, and social acceptance is a game of statistics and mass morality, really, so it doesn't matter what you as an individual think.

Also, swearing is lazy. People often swear because they can't think of more precise language to use due to a lacking vocabulary. This is a pretty broad generalization, but I have often found that those of lower socioeconomic class tend to swear profusely no matter who they are talking to. I'm not willing to draw correlations here but I certainly wouldn't want my kids emulating that behavior. Again, broad strokes so take this one with a grain of salt.

And finally, the fact is that expressing extreme emotion is often considered to be rude, odd, and very informal. Which is probably why swear words fit into the context they fit into. But kids don't really understand this kind of contextual behavior -- they say ANYTHING to ANYONE -- which is why I say kids should not have these words in their vocabulary.