#MetalGate exists because there is nothing that social justice warriors and radical feminists don't want to come and fuck up.
Just look at #GamerGate if you want to see their modus operandi in action.
Sources:
Yesterday's article
http://www.deathmetal.org/article/metalgate/
It's been happening since 2006
http://www.washingtonpost.com/wp-dyn/content/article/2006/08/10/AR2006081000925.html
Other articles
http://archive.today/ah7cr
http://www.popmatters.com/column/a-very-dirty-lens/
http://www.theguardian.com/music/musicblog/2014/sep/30/mastodon-the-motherload-misogynistic-new-video-sexism-metal
http://www.decibelmagazine.com/featured/we-like-girls-dont-like-metal/
http://blog.haulix.com/post/90375562700/the-gender-gap-in-heavy-metal-journalists
http://www.invisibleoranges.com/2011/05/are-you-talking-to-me-respecting-women-in-metal/
http://www.independent.co.uk/arts-entertainment/music/news/vag-halen-were-what-bournemouth-needs-say-canadian-lesbian-rockers-9775808.html