Before I go off on a rant here, Mimi has never been anything other than very nice to me. Because of this, I held my comments (beyond my intial sarcasm) because I wanted to say something but I didn't want to be hurtful toward mimi. My issue has nothing to do with her as a person, just the way she chose to deal with this particular situation.
If this were a situation where you were forced to accept a personal risk that you didn't agree to beforehand then your actions would have been justifiable. However, given that you were in your car, the risk their lack of helmets posed to you was relatively minor.
However, it sounded like these guys were grown men out for a ride. That means they were competent to make their own decisions about their personal safety and the risks they were willing to accept.
But, you chose to ignore all that and impose your own beliefs on them. Further, no cyclist likes having a pleasant ride interrupted by yells from passing motorists unless it's encouragement or warning about things like big, fast dogs, or pieces of one's bike falling off.
Put yourself in their position for a moment. How were you any different than the motorists that yell at cyclists for riding in the road?
re-cur-sion ri'-ker-shen n: see recursion