Don't change a thing, iluvsummer...if I had kids, I'd be thankful for a teacher like you who is appropriately stern and doesn't put up with the infinite poor behaviors kids will pull. The problem, of course, is that these behaviors are tolerated a) at home and b) in other (weak) teachers' classrooms.
Kids will try to pull any excuse (and most always blame the teacher) for not going to class. No wonder the girls felt uncomfortable when so many parents simply gloss over disgustingly crass behavior with a paltry time-out.
And I never thought of this, but you made an excellent point:
These girls will need to get used to dealing with different teaching styles as they go through life, and they also need to learn that it has nothing to do with them when another child is reprimanded.
People in our society complain and whine too much. I'm so sick of when out of the mouths of babes comes, "_______ makes me uncomfortable..." and hordes of counselors come rushing to them, saying, "There, there little one..." Bullcrap. Unfortunately, school is the only place some kids will ever learn things like how to socially adapt; life isn't always fair and no one promised you a rose garden; pull up your big-girl panties; and life isn't all about you.
Don't back down.