1) Being evil gives players a chance to talk outside the thread. You can post all you want without any of them wanting to twist it around and lynch you. It is fun being evil. Sometimes I am good at it, sometimes I am not. I also think the times I have been evil we have lost more than we have won. Being evil is also about being part of a team.
Most of the time I play as if I am evil, this keeps me from being hit as the evils will want to keep me around as a suspect.
I briefly thought about volunteering. I figured it was best to just let it ride, if I was given a role, then so be it. I thought asking to be evil would be asking for trouble. Also, when this game is over, we will know who asked to be evil - I think this will be interesting to know in future games. I would rather be recruited or picked randomly.
2) Is this a question? You sure it was not just one thing?