I'm happy to debate anyone who suggests that we 'lost' the war in Vietnam.
People tend to forget the tensions of the era, and the 'Communist vs Democracy' ideological debate that was happening at the time.
The first cab off the rank was Korea. That ended in a draw (which was essentially a victory. It halted the move south).
Then came Konfrontasi. Without intervention that would have seen Communism on our doorstep.
Then came Vietnam. If it had been accomplished without a whimper, how would south-east asia look today? Whilst the Communists might have eventually taken their place in Vietnam, the war there certainly stopped the movement in its tracks.
The war in Vietnam served its purpose. It stopped the spread of totalitarian Communism in Asia.