Wow. Just wow.
There's absolutely no evidence that Trayvon was a drug dealer or a gang member. And you shouldn't be assuming the worst of a kid that's passed away without proof.
He got suspended from school, he may have smoked weed, said some stupid things on twitter, and he could have been involved with a bit of petty theft. Those are things that plenty of teenagers do and it's worth pointing out that most of them still go on to be productive adults. They're kids and if we're going to live in a society that insists on extended adolescence, then we need to let teenagers make mistakes and figure life out.
Although Trayvon clearly wasn't a saint, we also know that he loved his family and that he had plans for college. If anything, this combination of good and bad more or less demonstrates that he was a regular 17 year old who was still growing as a person.
I, and I'm sure plenty of other people, would be extremely reluctant to live in a place where not being perfect -and therefore having the potential to hurt other people in the future- is viewed as a fine reason to shoot me dead while I'm walking down the street and then to not even bother investigating the details of my death afterwards.
Even if Trayvon had gone on to be a troublemaker, there's a legal system in place that would have dealt with his crimes after they happened. You don't get to pre-emptively shoot someone over what they *might* do in the future. That's not civilized behaviour and it sets a dangerous precedent.