Chill with the historical revisionism. The American revolution was a very important historical event. But it was NOT the first example of a western Republican government. Both The Netherlands and Switzerland preceded it. The process of moving the west away from monarchic rule was a long one with many important steps along the way. One of these was the American revolution. Which IMO was less influential than the French revolution in ending monarchy.
Switzerland has been a republic since 1523 at the latest, 1291 at the earliest. The Most Serene Republic of Venice was founded in 421 and lasted more than 1500 years. But France has a much, much better claim than either to have founded the modern republican movement. The idea that the US had more influence on early modern republicanism is risible.
There's no doubt that villains abound .. the question is, does the world need a "global policeman"? The historical record shows that these powers, even when acting with the best intentions, usually lengthen suffering where they intervene by distorting local and regional power dynamics. And more often than not, the motives for selecting a given site at which to intervene are less than scrupulous (Britain in India, US in Iraq) or are perpendicular to the host's interests (Vietnam), in which case there is no excuse for the resulting fallout.
After WW2, the US wanted a united front against the USSR. France used their membership in a Western European military alliance as a bargaining chip for the recapture of their Indochina colonies.
The US felt supporting France in Indochina was a lesser evil than letting Western Europe fall to Soviets.
The world in the 18th century was not -- and today still is not -- able to grow and nurture a powerful country towards "absolute moral good." The world is still a primitive and dangerous place full of despots at worst in inequality at best.
It's good to hold the US to a higher standard, but unfair IMO to critique with such loathing the way the OP did.
Finally: It's certainly true that many of the ideals of the American Revolution were inspired by European writing on the subject. Not surprising considering most colonists in North America then were Europeans themselves. We can never know exactly how the 19th century would've unfolded had the British Empire not been so immature and insecure with themselves. They were a relatively young world power and they seem to have believed in the same age old "Domino Theory" that still trips up the US today. Had they been more wise in their choices, they would've granted the colonies freedom from Parliament's authority in exchange for full economic participation in the empire. Most likely you would've seen this unfold over the 19th century and quite possibly maintain itself to this day. Had America been a Sterling country, the British economic situation during WWI & WWII would be so vastly different that it's hard to even speculate. And if that were the case, how would that have changed the pace at which democracy unfolds across the European continent and around the world?
I think it's easy and fair and accurate to argue that the spread of democratic and republican ideals was influenced and catalyzed by the 8 years of hot conflict during the American Revolution. I don't think you can over-state how inspiring a Saratoga or a Yorktown was.