Somebody gave me what has to be the first reason not to curse that I can respect:
"It takes no discipline to curse."
Except, personally, I disagree.
I grew up so shy, so self-contained, and so afraid of breaking the rules that cussing is a sanity check for me. If I let one slip and proceed to panic, I know I Need to Calm Down.
I had to practice to be able to curse, out loud, in front of other people. (I still would rather walk around pantsless than try to spit in front of someone.)
I still think cursing at someone to make them feel bad is repulsive. I do it sometimes and am repulsed. I feel embarrassed about cursing in front of someone who finds it offensive or improper (or excessive). I also feel embarrassed when a ridiculous number of cuss words show up in my novel - on the level of using too many exclamation points or adverbs. I feel like cursing in the car is losing my cool when I need it most.
But, in general, it takes me more discipline to keep myself relaxed enough to curse and not grit my teeth afterwards than to keep my mouth shut in the first place.