I think that there are no protests because for one, this is a voluntary military. Young people aren't seeing thier best friends being yanked to a foreign country with damn good odds they wouldn't be coming back. The casualty rate is also not as high as in that era.
And beyond that, there was no 09/11 before Vietnam so that people couldn't actually SEE the bogeyman.
Plus alot of the protests and hippie movement was about an "in your face" attitude and thumbing thier nose at authority and the shackles of society. It was far less about the actual war, but it was a good excuse to flip off thier parents.
Another reason: something besides the MSM is out there. We have talk radio, convervative news programs, the internet, and other means of hearing the truth. We don't have to rely on Walter Cronkite and his ilk anymore.