Remember the USA used some terrible "weapons" in Vietnam such as Agent Orange and Napalm.
http://en.wikipedia.org/wiki/Agent_Orange
https://en.wikipedia.org/wiki/Napalm
These have caused hundreds of thousands of deaths and deformaties in Vietnam since they were used.
Strange thing is the USA complain about what happened in 9/11, where about 3,000 people were killed, but the USA have been responsible for far more deaths and deformities with what they did in Vietnam and other countries.
In fact some of the things they did in Vietnam border on chemical warfare and terrorism.
And of course sometimes you reap what you sow and it could be said 9/11 was as a result of the USA's continuous abuse of its size and military might around the world.
In fact the recent documentary shown on BBC called "Oliver Stone's Untold History of the USA" comes out strongly against the USA "Military–industrial complex".
When Eisenhower left office in 1961 he used the term Military–industrial complex to indicate he felt that some people in the USA thought it was in their interest to have a strong military industry in the USA and to initiate wars around the world to justify the building of these weapons.
http://en.wikipedia.org/wiki/Military%E2%80%93industrial_complex
I think it was this Military–industrial complex and all that surrounds it that the hippies were complaining about.
Of course the drugs like LSD helped as well !