which was a threat to us... how?
Agreed. Their ideology was not the same. We were still fighting the "cold war", and had placed everyone who called themselves "Communist" in the same category - enemy. They weren't all the same. The Vietnamese under Ho Chi Minh were more like the founding fathers after having fought off the British than they were like the Soviet Union.
They wanted the war. Whether they manipulated the intelligence or not, I don't know. The fact is, the intelligence was flawed, and the war should never have been. That may sound like being a Monday morning quarterback, but I've said all along that the invasion was not called for, not necessary, should never have been.
or in the face of a clear and present danger.
True, and that alliance lasts until they are no longer useful. We were once friends with Saddam Hussain, for example.
That would seem to me to be the motive behind Iraq. It most certainlhy was the motive behind the invasion of Vietnam, but then, that was before the PNAC, so we can't blame that one on them.