We would have won in Vietnam, albeit in a different, more direct way than we eventually did (prior to forfeiting in 1974). We might have invaded the North or even nuked them. Most likely–and we are talking 1965 here–the credible threat to do so would have ended their incursions, and HUGE amounts of life would have been saved.
The Soviets would have done a lot of huffing and puffing, but even though propagandists lie for a living, that does not mean they do not know what the truth is, and the truth is that that war was ALWAYS, from the outset, an invasion by the Communist north of the non-Communist South. They know it is not OK to invade other nations.
We would not have had the Great Society or War on Poverty, although we might possibly have gotten Civil Rights legislation of some sort, but not as encompassing as what was passed. People forget that Goldwater was an early and enthusiastic civil rights advocate, and that he founded the Arizona chapter of the NAACP.
Nobody would have tried to save the blacks or poor. They would have continued to be forced to advance on the legs of their own effort, own ingenuity, own persistence. And they would have advanced, in fits and steps. They would have continued growing, integrating, becoming middle class.
They would have continued to encounter racism in the South, but this would have forced them to become so good, so well educated, that they either could not be denied, or were readily accepted elsewhere. Characters like that of Sidney Poitier in “Guess Who’s Coming to Dinner” would have become common, even expected.
Over some period of time of determined effort, had it happened, all the old “truths” of institutional racism would have fallen away, and blacks understood and welcomed as equals.
A growing economy would have raised all boats.
And when you get to things like the Oil Shock, and Iran, and stagflation, you have to go back ten years and wonder how things might have played out differently.
It appears the PLO was created by the KGB, so the entire military history of that region has to be understood from the basis of the Soviets operating largely unopposed in their propaganda and organizing. A stiff defense, and following victory, in Vietnam–and everyone understood even then this was a proxy battle for who was the more convincing and reliable ally–would have greatly diminished their recruiting efforts. We might not have seen terrorism grow to the extent it did. The coup in Iran, if the situation had even been allowed to get to that point, which seems doubtful, would have failed.
We would not have seen the slaughter in Cambodia and Vietnam and Laos that happened. There would have been no labor camps and no psychological torture camps. The war in Afghanistan likely would not have happened, or in Angola, or Ethiopia.
The Oil Shock likely would not have happened. As far as stagflation, I cannot speak to what the Fed would have done. They were largely uncontrolled even then, and following their success in getting the last vestiges of control removed, COMPLETELY free and unaccountable as of roughly 1980.
In short, a lot of good things would have happened. Slow progress does not make headlines, but seemingly neither does slow decline.