Hmm... interesting question....
I would think what makes it wrong is the fact that your cursing AT something, like, "Darn all this rain, we need more sunshine!"
Your cursing something, in this case, the rain.
As to what makes its synonyms ok or not is because they're not used as swear/curse words (cursing something) and instead are being used as nouns and verbs.
The 5 letter "B" word that is used as a swear word today use to just harmlessly mean a female dog.
Now, I myself find most of the synonyms vulgar and don't use them either, even if it's just their harmless meaning.
As in, I don't go around and call a female dog I see a "B" simply because that the simple pronoun of a female dog has been so commonly used as a swear word that in society's eyes it's always considered vulgar, but as I said, it actually technically is not.
Very good question Brian
-The Lowest Servant
EDIT: Sorry if that didn't quite answer your question.