Every development in heavy music is derided by mainstream critics. When Black Sabbath and Led Zeppelin emerged in the late 1960s, they were sneered at for their lumpen, troglodyte stupidity. A decade on, AC/DC were reviled for precisely the same reasons. When Metallica and Slayer helped lead the thrash metal movement in the mid-1980s, it was at first only enthusiasts for extreme noise who cheered them on.