The immediate suspicion is that they were leftists, possibly homosexual lovers and maybe influenced by the Goth youth culture. Unlike, say, Vermont, where there is little conservative cultural or religious influence, Alabama has a strong evangelical, and particularly Baptist, influence. The church burnings may have been their acting out of their hatred for that influence. Perhaps the ACLU has had the same thoughts, since they responded very quickly to the defense of the suspects.
Or maybe, since BSC is affiliated with the Methodists, it was a denominational prejudice. Methodists vs. Baptists.
Whatever it was, they've ruined their lives and their families's lives forever.