I admit that I am not an expert on the Vietnam War, but I have studied the war for a number of years (including two college courses on it) and have found my views on the war to be ever changing. However, one charge that I hear often disbursed is that the American government "lied to the people" about Vietnam, a statement which I am having a hard time substantiating. The argument that the American government lied tends to rest largely on two pieces of evidence. The first piece being the second Gulf of Tonkin incident and the second piece being General Westmoreland's statement that the United States was "close to victory."
While it is true that the second Golf of Tonkin most likely didn't occur, American policymakers and those in the defense/intelligence community believed that it did happen at the time. It wasn't until after the incident that doubts began to arise as to whether or not the second incident occurred. Even if the second incident didn't occur, the first incident certainly did; though whether or not North Vietnam's attack was "justified" or not is a matter of some debate (as one could argue that they were "retaliating" against a South Vietnamese special forces operation in North Vietnam).
As for Westmoreland's statement, one could argue that he was acting on "bad information" or legitimately believed that the United States was winning the war. It should be noted that Westmoreland went out of his way to stifle any and all reports that challenged the effectiveness of his policies. This leads to the second point, that Westmoreland was speaking largely of his own views when making that statement, rather than speaking on behalf of the United States, as he had personally destroyed the careers of anyone who questioned his policies.
Also, one could argue that perhaps the United States was "winning the war," as the TET Offensive had completely destroyed the Viet Cong as a political entity. Not only that, but when Westmoreland was fired for his midhandling of the Vietnam War, he was replaced with General Creighton Abrams who undertook policies more suited to winning the hearts and minds of the people. With the Viet Cong having been eliminated, there were fewer obstacles to pacification (a policy that was vastly expanded under Abrams). Abrams also introduced a policy of taking and holding ground, making it almost impossible for the Viet Cong to ever be reformed. Abrams new policies, as well as the policy of Vietnamization, were major steps in winning the war. Knowing what we know now about how devastating the TET Offensive was for the Viet Cong (and how it prompted Westmoreland to be replaced), perhaps Westmoreland's statement about the war was not entirely untrue (though not for the reasons he believed).
I believe I have addressed the two main charges against the United States government having "lied" about Vietnam, but if you care to dispute my two statements and/or have other major examples of the American government "lying about Vietnam," I'm open to hearing them.