Why is that so many of my role-playing persona have antisocial tendencies?
Because I’m such a nice guy, that’s why.
There, I hope that’s clear. If not, read on. You see, there are many possible approaches to developing a character concept. I should know—I go through characters faster than almost anyone I know. Partly this is because I take the roleplaying seriously. I have let characters walk straight into fatal traps that I knew were waiting for them, simply because my character would have no way of knowing better, and I couldn’t come up with any plausible reason why the character would act differently.
Admittedly, most of these characters come from my Friday night gaming at Mac’s. In her house rules, all character stats are randomly assigned, there are no re-rolls, and you play what you get. Such a system makes it easy to roll new characters—I can usually do it in 10 minutes or less with only minor consultation with a rulebook. But it also does not engender any character loyalty. When your character has one hit point and no stat higher than 9, you’re rather tempted to kill them off immediately. I treat my useful characters (eg. Analin the Ranger School Drop-Out) and characters that take a long time to create (eg. James Jadwin of Deadlands fame) more carefully. But I digress.
I’ve seen a number of attitudes towards character development:
1) hero fantasies – think of someone who only plays lawful good characters, who live only to do “good deeds”
2) ditzes – I’m not certain what the motivation is, but someone dear to my heart seemingly plays the same
character again and again in different milieu – the flighty, scarcely sensible Teabull under a variety of names.
(Maybe this is why Sor Teresa is such a refreshing change of pace—plus that sexy accent—grrrowl!)
3) competency – somehow this person’s characters always do the sensible thing, regardless of their intelligence
or wisdom stats, and always have just the right magic item stashed away in a magic sack.
4) real life – the one time that Rachel and I role-played with my father-in-law, he insisted on playing a character
with the same name, skills, and occupation as himself.
My own attitude is that I want to play a character as different from myself as possible. When I look back at the last three years of characters, I have perhaps played two wizards or mages in that entire time. I actively avoid them, even though I make my living doing the modern-day equivalent of magic, and intelligence is probably my defining trait. But after a week of slogging against quantum mechanics, Lagrangians, and code algorithms that just don’t work, the last thing I want to do on my weekends is play a smart, logical, problem-solving magic user, even though when I do play such a person I find them understandably easier to play. It’s just too BORING!
My favorites tend to be thieves and rogues. I would play them much more frequently if they weren’t so generally useless in typical game play, and if it weren’t so hard to come up a good rationale why my character keeps going on all these “feel good, do good” missions with the would-be heroes. I want a chance to rob, steal, and plunder, and to get away with it. Now I never engage in such activities in real life, but if I wanted real life, I wouldn’t be role-playing, now would I?
It’s actually not easy to be evil. The biggest problem is that my fellow gamers, or at least some of them, often tend to be do-gooders. (I wonder … if I want to play evil characters because in real life I’m so nice, what does that say about people who only want to play good characters?) I often find myself stretching to find some reason why my character goes along on the heroic quest, instead of just stabbing everyone in the back, and I probably wind up being a good deal less evil than I mean to.
I think it would be rather fun, actually, to roleplay with a group of criminals. Screw adventuring—our party’s aims would be to rob, steal, assassinate, etc., and to try and get away with it. Escaping from the cops, running from the town watch … what could be more fun?
Is it any surprise that my favorite video game is ‘Thief’?
Tales of the Rambling Bumblers 
I think it is safe to assume that my motivation for playing ditzes is the same as your supposed motivation — because I'm not that way in real life. I tend to think of them as “eccentric” more than ditzy, and I play them because it's fun. I think it's more important to me that we all be laughing than that we be remotely heroic.
Some of us play Good characters because we're so damned nice that we can't even comprehend evil peoples motivations. Me, for instance.
No, seriously, while my characters in Mac's game are all over the place on the Law/Chaos axis, they're almost always Good or Neutral because I just find it too hard, and too little fun, trying to figure out what makes my rare Evil character tick. The best I usually manage is Evil=Selfish, but in an adventuring setting that's often contrasurvival–which seems to be borne out by the fact that most of my evil characters die so fast that the other players don't even seem to be aware that I ever play evil characters.
BTW, another possible character development motivation is
5) Who cares? Being left out of the activities or PK-ed is no fun at all, so you might as well play someone who gets along with groups. That's generally easier to do with Good or Neutral characters.