Why do people carp about U.S. involvement in the Vietnam War.? The U.S. and South Vietnam were both members of SEATO (Southeast Asian Treaty Organization) so arguably the U.S. had an obligation to fight on behalf of South Vietnam from the beginning.. Not to mention the North Vietnamese attack on the U.S. destroyer in the Gulf of Tonkin (unlike the later August 4, 1964, attack which never actually happened the earlier August 2, 1964 attack most certainly DID HAPPEN as it was admitted to by the North Vietnamese at the time).
By any possible stretch of explanations, U.S. military action against North Vietnam was clearly justified.