I find it rather disturbing that you find it perfectly acceptable to share such detailed information about another person online - what right do you have to share his name and school??? And the fact that you looked up his history? That's by far more disrespectful than the things he was doing....

Your sister is clearly aware of who Matt is as a person. She accepts that, and obviously loves him enough to move to a new state with him. Good for her! Your opinion of him really doesn't matter. And no, your parents should not have tried to stop her from seeing him or moving with him - I am glad to hear that they didn't! It shows that they respect their daughter and her life choices, even if they don't happen to think it's the best decision.

You are judging him based off of his public profile - which sure, it'll show a lot about someone. But your way of judging is very harsh - you've even seemed to make the assumption that he went to that privte school because he was expelled from other ones. So what if he has tattoos and piercings? So what if he dresses like a goth? So what if he has ambitions that are hard to obtain? If he and your sister can afford to live their lives, then it's perfectly alright.

I wouldn't share your opinions with your sister unless you are asked. Personally, I'm absolutely furious with your judgemental attitude and I'm not related to you. I can't imagine your sister feeling less enraged than I am because it's her life and the man that she loves. You should spend some time actually getting to know Matt and taking some effort to find out what your sister loves about him. If she ever expresses some worries or doubts, you could then offer something to her... but really, it'd be best to just keep your opinions to yourself and try to find the good in him.