Not surprising
My experience is that people who listen to gory metal (or are outright fans or even take active part in production thereof) usually listen to all sorts of other things and are generally more accepting and more open to new and different things and views. Whereas fans of sterile pop usually listen to sterile pop only.
I run into metal guys quite often in the theatre or opera, into pop people not quite so often. So those saying that violent music brainwashes you or makes you violent basically sound to me like telling opera or classical theatre might as well cause the same, which thought is of course utterly ridiculous to those who say violent music does it for certain.