I tend to agree with this comment posted on a thread at Pharyngula (in reply to a suggestion that the best response to someone who clings blindly to a belief/worldview that is patently stupid is to be polite and try to reason with them)

Pat, ridicule and anger have a time-honoured role in social change. You’re confusing what is effective (sometimes) in dealing with people one on one with what is effective in changing the social climate en masse.

In many cases people’s idiotic beliefs are too entrenched to be amenable to reason, evidence, or polite discussion. The only way to prod such a person into reconsidering their views is to convey to them that those views have made them a laughingstock and/or object of contempt.

Attitude change is not fundamentally a rational process.

You want to be a "good ambassador" – a nice guy in other words. That’s a valid and useful role and it obviously suits your personality better than snarkiness. But the snark brigade is not working at cross purposes to you. History strongly suggests that their role is essential in softening people up for your more polite form of persuasion. The good cop needs the bad cop for the routine to work.

Name one social change movement that succeeded through polite persuasion alone. What you’re comfortable with is not the measure of what works.

In general I am extremely polite when dealing one-on-one with someone, but the less personal our connection the more likely I am to resort to tactics which may appear somewhat "mean". Rationality alone is ineffective against a person who’s already decided they hate everything you stand for, and although some people might say that resorting to insult will simply harden your opponent’s position, I can’t say I always agree. Certainly within a given exchange this is the case, but this may be merely a short term defensive reaction; a salvaging of pride. In the long run I think it’s acceptable to call an idiot an idiot, especially where that idiot would inflict their idiocy on others. Trying to reason with them when they have already shown disdain for reason itself is giving them a seat at a table that they haven’t yet earned, and can even serve to validate their position.

That said, I don’t think it’s an either/or choice; like the commenter above I believe a combination of rational and emotional approaches is required to really effect change. If someone makes me angry, it’s better for me to show this than to pretend I am somehow above this irrational side of conflict. Even if it seems to "weaken" my position, it’s more honest and ultimately more effective I think.