I personally don't mind if there is option to turn it off, but I really don't see the point why should someone buy M rated game and be considered about porm.
It's almost like you buy a porm and get considered by nudity.
Sure, there is soft core porm movies out there, but they do no good since nether will they get you hard (they are called 'soft' for a reason you know) and nether it will completely remove nudity.
Same is with gore here.
You'll be still killing people, but with gore, at least you can do it properly and with full satisfaction.
Also, gore will add weight to act of killing (witch it should) and will not make act of murder look like Super Mario turtle jumping.
There's more to maturity than explicit gore. The Mass Effect series or the game Xenogears are two great examples of this.
Some of us don't like to see it. I play a game to have fun and not be horrified by brutal explicit violence. Real violence is horrifying and not at all desirable. I understand it's fake, but I don't want the violence to be that real.
The "why play an M rated game if you don't like blood/gore" argument really does not work either. Gore and blood are superficial aspects to a game. They add nothing to the actual way the game plays, which is why I play to begin with. I loved Doom and Hexen and yet I didn't prefer the gore. I liked them despite the gore, and not because of it. I also played and enjoyed Eternal Darkness. Again it wasn't because of the gore that I loved the game but despite it.
Again I have nothing against people wanting it, but I don't want to have to see it. It's quite frankly disturbing to me that some people seem to gauge personal worth based on whether or not you want to see graphic violence.