They created a gamemode to be played a certain way.
I'm assuming your problem is that you can't see anything while being shot (or similar), but this is a gameplay element just like hiding player names.
Blood doesn't affect gameplay, what? It's purely visual, and there's plenty of games with an option to disable blood.
The "can't see anything while being shot" is default with the game (redding the screen) so that's irrelevant
The only possible issue is what Tony mentioned, where blood is a clue. And if you disable it there, you're hurting yourself, not giving yourself an advantage