Don’t think so. The drug culture happened outside of Vietnam and in many countries that weren’t involved in it. Goldwater’s election might have slowed the progress in the US, but even bailing out of the Vietnam War early wouldn’t have stopped it.
I was in the US Navy at the time. Both heroin and marijuana were reported in use in VN. (As was “fragging”).
Given TS clearance, and admonition to shun blackmail- and kidnap-exposure, I was astonished to hear a colleague trumpet the “highs” of MJ!
“Boldness” wasn’t a feature of President Johnson’s approach to VN.
“Bailing” wasn’t inevitable.