What kind of "meaningless violence"?
If you're playing a mature rated game, you should already be expecting that kind of thing. If the game is cartoon-y, the violence is so sugar-coated that one can always assume that the monsters are merely knocked unconscious.
Please clarify.
Hey i like things going splat, i love meaningless violence to people and farm animals(The kind you eat)
Dogs are just a special case for me 
I love games with some humor but not the "LOL DOG/CAT GOT RAN OVER AND LOST HEAD OLOLOLOLOL" kind of "humor"
I dont want a toggle button for violence, Hitman did that enough. I just want a new PEGI indicator for violence to animals.
Its obvious that a shooter would include atleast a bit of gore and meaningless violence, but its not always obvious that you will have to kill a dog too, unless its called "Dog Slaughter Sim 2003"
"Violence to animals" is covered under "mild/cartoon/strong violence", at least here in the States with ESRB. If you so much as slap a gorilla in the face with a paper fan, you get some level of violence tacked onto the rating.
Why should dogs get such special treatment?
(big) Cats are frequent targets, as are birds, bears, warthogs, rodents, and reptiles. Is it just because dogs are "man's best friend"? What makes dogs, even monster dogs that try to rip your face off, more deserving of (virtual)life than other humans?