Swearing does not add nor substract emphasis; it is punctuation, placeholder words that might as well be onomatopeias.

At least for my own speech, profanity is primarily a way to add emphasis. This seems to also be true for a significant fraction of the people I've known.

Of course, profanity is not the only available source of emphasis. There are still lots of ways to convey emphasis with the level of profanity held constant.

There's absolute emphasis ("Listen up, because I will only say this once" draws extra attention to the entire statement that follows), and relative emphasis (the word "constantly" in "...a character who swears constantly and still..." is emphasized more than its neighbors, regardless of the level of passion it is read with). You can get someone to pay more attention in general, but attention paid to one thing is still attention not paid to something else.