Say, rather, that to start (or continue) a war that leads to the death of millions in which you fail to "save from Communism" those not blown to bits is a horrible and criminal mistake.
I think historian David Kaiser has put it best:
"... the Christmas bombing.... There isn't a shred of evidence that the Christmas bombing was necessary to get Hanoi to sign the original October agreement, which is basically what we both signed after it was over. Mark Clodfelter, Larry Berman, and indeed, everyone who has investigated the sequence of events clearly has concluded that the bombing was designed mainly to convince the South Vietnamese to go along, as well as to express Nixon's frustration over having to settle for much less than he wanted.... Under the Geneva Accords of 1954, the question of whether North Vietnam "had a right to conquer South Vietnam" was meaningless: those accords, like the 1973 accords, recognize the unity, sovereignty and territorial integrity of Vietnam.... Americans [in the absence of United Nations support] have no right to decide who should rule them and impose our choice by force. If a regime is sufficiently cruel, it may be necessary to overthrow it, but in a case like that there should be no need for us to undertake the job alone. In 1965 there was obviously more support for the Viet Cong in South Viet Nam than for the Saigon government, and our attempt to make the Saigon government prevail killed, literally, millions (certainly well over one million) without affecting the result. As such it was a terribly unwise move. Whether our intervention in Iraq will leave the Iraqi people in a better state is, at this point, an open question. I hope that it does."
Brad DeLong