You guys are opening up a whole new can of worms. If you want, we can go off into whether or not people who succumb to their environment and act as they were raised too are evil or not, or if people with mental disorders such as Anti-social personality disorder or Schizophrenia are inherantly evil, or if they are just horribly twisted because of their genes and parents. Can you really blame someone who was *born* without being able to feel guilt or regret and with a genetic predisposition to harm for their actions? It's like accusing a mentally handicapped person of wanting to be stupid.
People throw around the word evil way too often. The bottom line in dragonball Z is that there were some guys who wanted to hurt some people and get some power and there were some other guys who decided it was in their best interests to stop them. Don't read more into it than that.