This statement is false.
It is not true that most important issues have been addressed - this is very wrong because not much attention is being paid to global warming, as well as other pressing issues. And even if it were, America is always trying to correct the wrongs in the world, so there will surely be more turning points in the future.
The Vietnam War faced mass opposition for several reasons inlcuding:
1) Unfair draft practices- Many citizens who were affluent and had connections were able to avoid being drafted by the US military. This resulted in a majority of the soldiers being individuals from lower-middle class socioeconomic groups. Many citizens felt that this was unfair, an dubbed Vietnam a rich man's fought that happened to be fought by the poor.
2) Monetary cost- The Vietnam War cost America billions of dollars over the course of the 2 decades of their involvement in trying to keep South Vietnam out of the control of the Soviet Union/communism.
3) Casualties- The US military suffered over 50,000 deaths due to this war. Americans felt that this was unacceptable.