curse words

Why are some words acceptable or permitted for a Christian to say and some aren't? For example, the word ass has always been frowned upon as being derogatory - resulting in a spanking when I was a child. That is one of many so called profanities which many Christians are told growing up are curses and should not be said. There are other words, which I have always felt guilty about saying, yet have more recently slipped out on a regular basis for various reasons. So why this guilt? Why this teaching that these words are bad? Not until I was in Bible college did I hear the argument that these words are not swear words. Swearing, this person said, was simply and only taking the Lord's name in veign. That makes sense doesn't it? Besides, these certain words actually do relieve stress when voiced out loud.
Right now I could sit and cuss worse than a sailor in a storm, but why? what would cause me to want to say these words besides the fact that I'm just a miserable, self-pitying, lonely, and angry person? I don't know. I was going to just type them out numerous times, but instead I've written what you have read thus far. And that is all I'm going to write.