Apart from having no "gestures / facial expressions" in online conversations, an other important factor is: There is little or no stake in being impolite in the cyber world. Most people online don't know each other in the real world. There is little consequence and also no embarrassment that would happen in real-life interactions. Therefore, people can really show their nastiness or aggressiveness behind the pseudonyms. At worst, just change another login name. Then why bother to be nice and friendly?
It is not surprising that people who use real full names in their online persona are usually more responsible and friendly in the way they speak and present ideas on the internet.
I have always used my real name on the internet, as I feel it's the only proper way to behave. Publish and be damned. However, that hasn't stopped me being very short with those that I consider deserve it, just as I would in 'real life'. I don't suffer fools gladly, or hardly at all, and at my age I don't give a rat's arse who I upset if they justify it. Equally, I don't see any point in being rude or unpleasant for the sake of it, so generally, I'm not.
The problem comes when on-line, on audio forums, that there are just too many know-nothing idiots, who take the view that 'I heard it so it's true' and don't know and don't want to know. I used to get upset and try and call these people out, but these days, I just shrug my metaphorical shoulders and can't be bothered to reply. They are idiots, and idiots they will remain. I won't change that.
Whether I would be any different if I hid behind a pseudonym I can't say, as I never have. However, sometimes it's tempting!
S.