What the French, toast?

What makes the bad word bad?
The only reason why people swear is because society makes such a big deal about it. See, if "shit" meant "nucleus" then it would be substantially less prominent in everyday vocabulary. People like to use powerful words to make powerful sentences, the most powerful of course being the most vulgar. But who gives these words such intense meaning? Only the people who oppose it, of course. If religions and businesses stopped caring, if parents taught their kids to say them, would they still be considered bad?
Another peculiar thing about swear words is that their equally vulgar synonyms are perfectly fine to say. What makes "nucleus/shit" worse than "feces"?
Scientists have to call it something, I suppose.