I believe Kissinger has said that the Vietnam-era protests kept the gov. from escalating the bombing of Cambodia, Laos and Vietnam, which presumably means that because of the protests fewer people died. I would say that counts.
You might reply that the Iraq protests are not big enough to do that. Neither were the Vietnam protests in 1966 and 1967. Eventually more and more people stopped believing the lies and became more comfortable standing in opposition to pointless violence. Hopefully the same thing will happen, and soon, before more kids die.