Why did the vietnam war happen even though a lot of people opposed it?

The Vietnam war was not really opposed in the beginning of the war because it was a different generation of people and those people hated communism and wanted to prevent as much as possible. There was a thing were if the U. S dint fight communism, there would be a domino affect. If china became communist and then north Korea. U. S would have less influence and would basically lose the cold war if they would fight communism. If one country becomes communist then the countries around it will follow.

Explanation:

the war in Vietnam started getting bad looks and Opposition when the war took longer than expected. its like staying in Iraq as america on large scale war for 20 years. 2.7 million soldiers served in Vietnam war and only 192,00 soldiers served in Iraq war. People starting hating it when it was an impossible guerrilla warfare. The only way to win it was to kill everyone and bomb everyone and building you see but this would be a war crime.