I just looked at the original script for Blade Runner, which was one of the original inspirations for Mass Effect besides Star Wars/Trek. In my head I started editing out all of the stronger language in that movie. Just like ME, there isn't a lot of strong language (just counted 4 f-bombs, 12 s-bombs, and one use of BS for the entire movie,) but what there is adds emphasis to a critical scene or moment.
Blade Runner is a dystopia sci-fi based upon our potential future, much like ME (only ME tends to be even less bleak overall,) and to take away those words and make things more sanity doesn't work for that setting. ME isn't a full-blown dystopia like Blade Runner was, but even still, life isn't happy and shiny. Language shouldn't be either.
That said, I wouldn't mind seeing more "alien" curse words. Even the roughest of language can tell a person a lot about another's culture. It's interesting to see what would be considered an insult in an alien language that sounds outright innocent in galactic. If a word or phrase is considered foul language in a culture, then there is usually historical reasons for that. I think it's a neat way to expand the lore some, as long as it's in small doses of course.
Also, I would enjoy if someone drops a commonly used curse word like the f-bomb and have the alien be confused. Cue the PC awkwardly trying to explain to him why these words are considered inappropriate in our society. 