To Flame or Not to Flame? Is that Even a Question?

Why do people flame others for having opinions? I never get that. The internet venues I use to meet people with similar interests are, at least in part, designed to promote interaction and discussion. This is the very essence of what this sort of venue is all about. Heck any personals venue (Craiglist, Match.com, Partners.com, etc.) is designed for the specific purpose of 'advertising' for what you seek (or at least what you hope to find). So, I am always surprised when a user takes it upon himself to flame another for holding a differing 'opinion' or seeking a particular type of person. I have things of which I am certain (I hate onions, and detest facial hair on younger guys). Does that make them 'right', no. It just makes them right for me. So, while I may question what someone else says or believes, I'd never be so ill-mannered as to attack them personally for holding a thought or belief different from my own. Don't these 'flamers' have lives? Wouldn't their time be much better served chatting up folks with similar or complimentary interests, rather than bitching at people who don't?