To be honest, there is no valid reason to go out of your way to avoid swearing. A person's irrational fear of particular syllables is actually a cultural phenomenon, an aspect of the super ego, the part of your subconsciousness which retains a system of ethics based on what you were taught by other people, rather then by natural instinct.
So, people decided that certain words were vulgar; probably because of what they mean (shit=feces, fuck=fornication, ass=insult but lat3er also buttocks, etc.). Noble casts refrained from using these particular words because it helped to separate them from the lower casts, who were usually less preoccupied with their social appearance. Imagine a haughty mother telling her child not to use such an unladylike word.
As generations came and went, the perception that these words were generally only used by the working class (the lower tier) became more common, and more often would children be taught that said word is the wrong word to use. After all, your not a peasant, so you shouldn't speak like one. This, added with the likely punishment which would accompany the use of said words, would establish itself in the child's superego as "Bad words = words that are bad."
The superego a person develops at a young age doesn't just go away; if anything, it strengthens over time. so, the concept of a "Bad Word" firmly plants itself. When such a child becomes a parent themselves, this perception is naturally passed onto their own children. Think "How could you say that word? That is a naughty word!" followed by punishment, just like the parent was punished as a child.
Eventually, after generations of this aspect of the superego being passed from parent to child, bad becomes naughty, naughty becomes dirty, and in the end, no one really remembers why this is a bad word, only that it is a bad word. Further, this negativity eventually establishes itself as part of a collective superego, meaning that it is applied to other conceptions of right and wrong, meaning people associate it with other similar superego values, such as religion. (please note that I am not invalidating religion, I am only mentioning that religious values learned from church and parents root themselves in the same way, as are basic values like "Brush your teeth" or "Stealing is wrong". so please take no offense.) Think "My, what an ungodly word!" (My grandmother XD)
Err.. Long story short, there is no ethical reason not to swear, short of the fact that it might insult another persons superego. Continue to swear or not swear as you see fit, as long as you don't jump down another persons thought for doing it.
Also, if you don't like Freud, then this wall of text is invalid XD.