It depends on what you mean by "swearing". If you're simply talking about language others deem offensive, it would only be a sin if you used that kind of language around them, not that you use it at all. Intent, of course, does play into it, and there are circumstances that private usage of such words could be considered vile, but that would be left to the individual's intent on using said language.
Overall, however, the words are not sinful, and even just the usage of them isn't necessarily sinful, although it can be. Most of the words we consider to be "swearing" had much different usages years ago, but due to being 'misused' (this is in the eye of the beholder, though) or connected with a certain group of people (typically uneducated or otherwise undesirable company), the words became offensive.
It's entirely subjective. The verses in the Bible condemn offensive language, which is not some objective list of words that are always forbidden, and for that matter, depends entirely on the culture itself. There are words in other languages which, when translated to English, would necessitate using a "cuss" word, due to the severity of the concept being expressed. However, in whichever language it came from, it isn't offensive, it's just a superlative.
I mean, if the words we consider offensive nowadays were rendered inoffensive, there would be a new set of words which would be considered "cussing".
So in short, it depends on the people around you, and it depends on your intent on using it (if you are the one using it). As has been pointed out though, sometimes the context of using such words is what makes them appropriate, for that particular situation.
As for me, I generally don't use the standard seven or their variants, along with a couple of indecent sexual references. If the situation warrants it, I will quote verbatim (with the exception of one variant in particular), but I very rarely use those words of my own volition. I don't generally get offended by them, though (unless it's excessive or completely insulting). I just prefer to use other language.