Which of these groups was most consistently opposed to the Vietnam War by the late 1960s?

fathers

hippies

doctors

professors

The U. S military had an escalating role in the Vietnam War and this created a marked opposition amongst many communities in the US. This conceived the first mass movement against a war in American history, a campaign that was led by several members of the society including but not limited to: students, anti-establishment hippies, African-American civil rights pursuers and women's liberation supporters. Further engagement in the opposition arrived from various groups such as professors, academics, lawyers and doctors. However, the most important role in the anti-war movement was played by the Hippies, who were born into a new generation produced after the World Wars and Great Depression that created individuals who refused and rejected mainstream American values which lead to the emergence of the counterculture.

The Answer is hippies