Some of you might find this a noobish question but does the rating have to be sex wise? As in anything that doesn't involve sexual content is safe? (even if it contains things that are extreme; drugs, alcohol, gore, etc.)

I consider images that portray extreme violence to be explicit. Drug use could be questionable I suppose, along with harsh language in dialog. Don't think this has been addressed before.

I wasn't aware that extreme violence and drug use and the like were restricted to only be viewed by 18+/21+ year olds, which is what I assume the explicit rating covers.
But then again, I just follow the site's ratings help page on this matter. http://e621.net/help/ratings

Unfortunately, that only covers sexually explicit images, not explicitly violent images, so it doesn't help here.

My own opinions on restrictions of this sort are that it's the violent images that should be kept to older audiences, not the sexual ones. I mean, if I had kids, I'd rather they decide that fucking, not killing, is cool. Anyway. I think it'd be reasonable for the Administration to have a pow-wow and see if some guidelines for rating violent (read: extreme gore) images can't be decided upon.