In answer to the question that led to this thread, any rational and informed argument to form an opinion on being "anti" anything is necessary yes. When we look at the examples of burning churches then we are firmly beyond the realms of rationality. We get into the area of fanaticism, incitement and arguably terrorism. I've just read an interview with Satyr (from BM band Satyricon for those unsure) who said that the whole controversy around the BM scene was down to a very small circle of people with a conviction to not just sing about their philosophy but a determination to act it out also. Others were just drawn into the circle by stronger characters who made no attempt to make them understand the extent of what they were involved in. The need to belong to something extreme, to feel a part of something that represents your anti political or anti religious beliefs isn't necessarily satiated by the music or lyrics of certain bands for some people and they resort to random acts of violence or vandalism.
Whilst I agree with the "giant middle finger to the norm" mentality of metal as a music format and how attractive that is to people (especially the young) there is a limit. Alice Cooper for years has used shocking theatrics to deliver his performance and generate interest in his music but he has a limit still. The lyrics and imagery of Slayer have suggested penchant for the darker side of beliefs and derision for traditional values of religion, but they have never professed to be Satanists or moved beyond using their music as a platform for their opposition to or questioning of religion. There is an important distinction to be made between using dark art and lyrics because you think it is cool (which isn't my view) or a gimmick and using such formats because it's what the artist/person genuinely believes.
"Anti" religion is valid as a standpoint, it's how it is delivered that determines it's overall relevance and acceptability. In the same way you should be allowed to express your christian, islamic, etc views through your music also. If you don't like it then don't listen to it.