On the American Revolution as a mistake -- without it, America would be more like Canada, with a parliamentary system which would have been more attractive perhaps in the 1870s after the British undid their 'rotten boroughs' that planted huge numbers of flunkies of George III in Parliament at the time of the American Revolution. America's Founding Fathers excoriated the British Parliament, an eminently reasonable attitude of the time. But after the American Revolution, the British removed some of the objectionable features of its representative institutions by implementing a Census that apportioned Parliamentary seats more connected to population.
Women's right to vote -- American and British women got the right to vote at roughly the same time. That is a wash.
Slavery? I am tempted to believe that Lincoln was going to do in America what the British had done a generation earlier -- compelling slave-owners to sell their slaves to the federal government which would then release them, and let the freedmen settle in the West. In view of the cost of the American Civil War, that would have been a win-win situation. But hindsight is 20/20 in history... In any event, there was no reactionary response analogous to Jim Crow in the British Caribbean colonies.
Perhaps had America been a Commonwealth country (or mostly Commonwealth countries), the outcome of World War I would have been different; a world without Hitler and Stalin would seem a nicer place in which to live.
This said, the American Revolution was practically inevitable once George III tried to micro-manage colonies which had largely been left to their own devices and already had well-working legislative bodies. George III was simply too rigid to do the right thing. Personalities matter in Crisis Eras.
We can all play games of "what if" in history. A not-too-bad President and Congressional leadership doesn't cause us to ask basic questions about the nature of our government. Donald Trump in collusion with a Congress best described as lobbyist-dominated causes liberals at the least (and maybe some conservatives like George Will and Steve Schmidt) to ask such questions. But people who think that Obama was born in Kenya who proudly wear "Make America Great Again" caps do not now ask those questions. I will say no more of that because I don't want to make it an issue of cognitive talent or proclivity.
DK's Comment on pbrower's comment:
PBrower,
I think your argument is completely ahistorical. It was the victory of the colonists on a democratic platform that gave democracy a long-term push in Europe. Without that victory Britain certainly wouldn't have reformed Parliament any earlier than they did. Nor is it clear that Canada would have benefited from the Durham report or the British North America Act. in any case--great historians don't argue with hsitory.
I think your argument is completely ahistorical. It was the victory of the colonists on a democratic platform that gave democracy a long-term push in Europe. Without that victory Britain certainly wouldn't have reformed Parliament any earlier than they did. Nor is it clear that Canada would have benefited from the Durham report or the British North America Act. in any case--great historians don't argue with hsitory.