And another thing I don't get that people do? Throw revive syringes in the MIDDLE OF A GUN FIGHT!!! Why waste the supplies when all you're doing is signing the guy you're reviving's death certificate? All that's gonna happen is they're gonna get shot before they can revive, and now you're a man down at the objective, and have less supplies to revive the next guy, or buff the objective class's health. Push the enemy back BEFORE you throw the syringe for cryin' out loud! If you guy doesn't have downed fire or isn't the objective class, 90% of folks, INCLUDING the AI will leave them where they lay. So you knock the enemy back some, then toss him a syringe, and now you're in a better position to push forward. A little tactical planning goes a LONG way. But I guess that's why these people ain't in the armed forces, because if they were, we'd run out of flags to give in condolences to their families for them getting themselves AND their squad mates killed.
It works, though. Its very effective to revive bodies in the middle of chaos, and the team that is constantly doing it usually wins that skirmish. I'm sure you've been frustrated before when playing against a self-reviving blob of people, and there are too many targets for the little amount of ammo you have before you need to reload.
Its one of those places where what is effective in game is drastically different from what would be effective in real life. Sort of like KZ2, where engineers sacrifice their life to plant turrets...and go 5 minutes without firing their gun, because they just keep respawning, placing a turret, dying, respawning, placing a turret, dying... It sounds ridiculous in real world logic, but its what worked in game.