My brother served three consecutive years (36 months from 1966 ~ 1969) with only enough time off to heal from three wounds.
He told me he finally realized who the real enemy was when he got off the plane at SFX and the freaks were throwing buckets of human feces on the Marines as the ran across the tarmac.
Another comment of his: "I would have killed as many of them as I could have if I had had my 45 on me."