How we cite our quotes: (Paragraph)
Quote #1
Whereas these attackers are part of a deliberate and systematic campaign of aggression that the Communist regime in North Vietnam has been waging against its neighbors and the nations joined with them in the collective defense of their freedom […] (3)
Consistent with the entire Cold War, Congress is trying to put America and freedom together on one side of the battlefield, and communism and tyranny on the other. Notice the word choice here, where Congress calls on America to defend freedom. Such phrasing makes it very clear where the two nations stand, and the goal here is to make America (and America's actions) the good guys. Most people would agree that freedom is better than tyranny, so the more Congress can appeal to a sense of freedom, the more acceptable their actions will seem.
Quote #2
Whereas the United States is assisting the peoples of southeast Asia to protest their freedom and […] desires only that these people should be left in peace to work out their destinies in their own way […] (4)
Now here's some patriotic freedom talk for you. Subtly referencing America's own history of becoming a nation through the fight for rights, Congress is clearly putting the U.S. on the right side of history here. By talking about leaving these nations "in peace to work out their destinies," Congress is making it look as though U.S. involvement is simply to help other nations gain the same freedoms that Americans enjoy. Of course, they're also implying that without U.S. help those nations will be stuck in tyranny.
Quote #3
[…] the United States is, therefore, prepared […] to assist any member or protocol state of the Southeast Asia Collective Defense Treaty requesting assistance in defense of its freedom. (6)
If it wasn't already crystal clear, America is on the side of freedom. But that's the point—by repeating over and over how this is a fight for freedom, against tyranny, Congress is winning over the American people and the international community.
By making involvement in Vietnam purely about helping other countries defend their freedom, Congress doesn't have to go into detail about how the true goals may involve other issues that might not be as popular to voice out loud (blocking communism, setting up a defense against communist China, etc.).