Overly gory, violent, perverse and blasphemous lyrics still have their place. Largely in an escapist viewpoint where one can vent and thrive in the primal adrenaline rush such can provide. That said, there can be well written examples of such, and absolute gutter trash examples. When it comes to brutal death and slam it falls into the gutter trash category more often than not. It's pretty hard to argue that, even from a subjective viewpoint.
As for the lyrics not meaning anything, I don't know about some of you guys, but any music that actually sticks with me which has lyrical content...I familiarize myself with those lyrics, to the point that even with the most perverse growls, it is recognizable to me. For the same reasons I stated above, it is therefore important for the material to be at least semi well written to effectively enhance those feelings.
The only exception's I have with this are a select few acts that sing in a foreign tongue i'm not fluent in. However in the majority of those cases the music is of the atmospheric variety, and thrives off of different qualities.