I think there is little doubt that Vietnam was a mistake- but I don't think it can be said that the protestors improved the situation. They certainly didn't help as far as informing the public or in reaching a dipomatic solution- they *might have* curbed a tendency to escalate the war- but it would hard to convincingly argue this point. What seems pretty obvious is it resulted in low troop morale and prevented the military leaders in winning the war.
As far as the current protestors, I don't see them having much of a bad effect- other than perhaps cause Saddam to misread the situation. I think the positive aspect is it might make our leadership be more cautious in how they enter the war and deal with the after the war situation more seriously.