It's not an option to turn on blood, it just makes YOU bleed when you get hit enough, meaning you have to apply bandages, taking you out of combat for a few seconds.
My impression of this demo can be accurately summed up in one word: stupid. Throwing dozens of guys at you, and you seem to be the only one who can hit anything from more than six feet away? Stupid. Making a game that uses over 900MB of memory, no matter what your settings? Stupid. A smack with the butt of your rifle does more damage than a bullet to the head? Stupid. Sluggish controls despite v-sync being enabled and a high framerate? Stupid. Watching the medic inject a syringe into thin air like your body was actually there? Stupid. Shooting plane after plane with a mounted machine gun, with a lack of feedback sounds or visuals to tell you you've scored a hit (except the explosion when you've fired off enough rounds)? Stupid. EA? Stupid.