My point is that people are more likely to listen and be moved by someone that they think is trying to help them rather than prove them wrong. This has nothing to do with arrogance. It has everything to do with being human. No matter how wrong we might be about something, I'm sure all of us would prefer to be told in a nice way that we are wrong, and why. No-one likes to be spoken to like they are stupid. No-one likes to be talked down to. This applies to athiests, Christians, the non-religious - everyone.
While I don't disagree with you (I mean, how could I argue to defend anyone's being a jerk, LOL!), I'd like to believe that for some people, the ultimate criteria to be used is not the cosmetic superficialities, politeness, social skills, but in fact, THE TRUTH itself. It's like in picking a president, I don't want a down-to-earth candidate who I'd like to have a beer with: I want someone who gets the job done!
I know people who disregard anything that Richard Dawkins says, as they point out how pompous the guy is (the British accent doesn't help). But the fact is, I've known people who truly WERE brilliant, and knew they were: they had little tolerance for dim-wits who drained them of their energy, and didn't put up with it. So anyone who dismisses a Richard Dawkins MAY do so, but it's only to their own detriment: the guy has forgotten more about biology than they'll EVER hope to learn.