Ugh, I grew up with people telling me about the evils of rock, hard rock, and heavy metal. In my estimation, 99% of it comes from misunderstanding and, hence, fear. Very very very few metal bands are truly Satanic. Some bands to have what sounds like anti-Christian lyrics and an anti-religious outlook, but you really have to dig deep to get to the true meaning of a lot of these songs and a lot of songs can be interpreted in many different ways (which is the intent of most artists). Many of the themes that are taken as anti-Christian reflect the lead singers own struggles with faith and spirituality. Lastly, some artists are telling a story or trying to shock. It always surprises people when they learn that the lead singer of Slayer, Tom Araya, is a devout and practicing Roman Catholic. Zakk Wylde of Black Label Society is also a devout and practicing Catholic. He often attends Mass while on tour. Ozzy Osbourne and a few members of Black Sabbath are Anglicans. The list could go on and on.
In my estimation, if your faith is so weak and fragile that a heavy metal musician makes you outraged, then your faith is not strong to begin with.