If you are actually trying to convince anyone of anything, being mean is generally pointless. You can be blunt, direct, harsh and a lot of other things, without actually being [I]mean[/I

If you are actually trying to learn something, expand your horizons, possibly even open to changing your point of view, then being blunt, direct, etc. is generally a bad idea, because these qualities are usually closely tied with being on defense or offense, and it's very rare for any person, ever, to admit that the other party was right, in such situations, even if they deep down know they are wrong them selves. Don't put your self into a situation where you might have to admit defeat, because the mere fact that you have to admit defeat, means that you were not actually out to learn anything in the first place. You just wanted to tell other people that they are dumb, or convince them that you are right, either to cement your security in your own ideas, or simply because you like it when people believe what you say.