it depends on what a person thinks, I don't believe in Satan jin win etc, they are mere delusions, just as many people have God/Gods they have satan, as long as they don't interfere in people's lives i don't have any problem with any satanists , Some of them systematically insult religion & the violence & misery it has caused... http://www.youtube.com/watch?v=raerE_zUfCA
then there are people who talk about the 'dark mentality' like that song 'fateless by R o t t i n g Christ'
& then of course there are people who depict the dark side of life with those Anti Human ideologies(Depressive Black Metal & Depressive Suicidal Black Metal)
Don't listen to 'em they are haram & they can dent your faith lol
PS: Nothing happens though there are people who had mental problems & were seriously delusional (e.g. there was a vocalist who had a mental problem in which a person is deluded to believe that he/she is dead, I forgot his name sorry) But nothing happens its another case that if u ended up with DSBM band then you are going to have some problems
hey hi,i was just typing on 'dark waves' profile and during read your msg to her that ''most of metal bands practice satanism''(i hope you don't mind if i am interfaring.)not only black but most of the metal bands are practicing satanism as 'slayer's vocalist is on record saying ''i am worshipper of satan'' and yes you will indeed have a bad effect on you as many of their lyrics are aggressive and promotes violence,even some people either commited suicide or killed other due to influence of it.even i have found change in myself since i started listening to metal.