As I stated earlier the My Lai massacre was bad, but in no way was it part of an official policy from the American government.
My Lai wasn't official policy, however AFAIK it
was official policy to clear villages - burn the buildings, burn the food supplies in case the VC used it, force the civilians out.
IIRC, there's a quote from one soldier who took part in them - he said from his personal experience, before these clearance operations civilians might not be pro-VC, but after them they were
definitely pro-VC.
Which, I think, is definitely one major reason for American loss of the conflict. Their methods of fighting the war ended up alienating substantial amounts of the civilians they were supposedly fighting to protect - I mean, if your home and your harvested food have been burned by US or ARVN soldiers (and if worse stuff happened during the clearance), then odds are that VC propaganda will look a lot more appealing...
EDIT: Hell, General Westmoreland
complained that the Australian units were only searching rather than destroying villages - the Australians were aimed more at bringing villagers onto their side by being more light-handed. And...when you consider that the VC were far more afraid of the Australians than the Americans, I think it shows who had the better idea of fighting the war.