Interesting news day.
It's funny really. Apparently, some people are getting all up in arms that The Black Dahlia Murder and Toxic Holocaust are playing at a Christian teen hangout, referring to the bands as "satanic metal" bands. I'm not totally sure of either band's religious leanings, but I can make a pretty good guess that they are NOT satanists. Honestly, some of their lyrics are a little questionable and possibly a little violent, but for the most part, both bands are a bunch of goofy metal fans that formed bands to pay tribute to their influences. They're people having a good time doing what they love. They're not sending any messages with their music.
Ultimately, I look at metal music for the most part the same way I look at horror movies. It is entertainment, no more, no less. Some bands may have beliefs that they try to push on other people, but the vast majority do not have an agenda.
Parents are free to tell their children that they don't want them going to a concert just as they have the same right to tell them not to see a movie, but in the end, it's probably the choice of the teens to go or not. Protesting concerts for some reason has become somewhat normal in Christian communities. You don't hear too many examples of them protesting movies like that though, probably because it wouldn't make any difference. Why is music different then?