Right because the draftees were YOUNG and right out of HS. They had their whole lives ahead of them and "no one wanted to be the last man to die in Vietnam."To be more historically correct, most of the demonstration against the war in Vietnam wasn't really about the war but against the draft. When the draft ended, the demonstrations died out but the war continued for for another two years.
The Pentagon Papers, Kent State and My Lai finally turned the public against the war. No doubt the way the US withdrew and the last flights out of Hanoi left an indelible mark on a lot of people, especially conservatives. I suspect they wanted to prove they could do it right the second time with Iraq. But the end results were same. Thats twice in my lifetime that our country has been misled into war. I will never doubt the power of propaganda to mislead a country into war again.There were the political left activist including the (New Left) in Congress who opposed the war in Vietnam, but they actually opposed the United States winning the war in Vietnam.
Should be noted that when the last American combat forces departed the RVN in 1973, every province with in the RVN was left in control of ARVAN forces. They would lose control of Vietnam when the Democrats in Congress in 1975 cut off all funding to South Vietnam. That's when NVA tanks rolled across the DMZ and it's pretty hard to stop an invading army when ARVAN troops were having their ammunition rationed at three rounds per day.