Asklemmy

If you just want to limit it to Haiti, Cuba, and the USSR, then yes each of those revolutions led to a vastly more humane society than the previous one. It also depends on who you're asking. Tsar Nicholas II certainly didn't see the Soviet Union as an improvement. Cuban plantation owners with dozens of slaves didn't see socialism as an improvement. There are winners and losers in history, the losing side usually isn't going to be pleased.

And who loses in a revolution? In a successful socialist revolution it's the capitalist class, colonizers, slavers, the previous bureaucracy, regional landlords. The USSR went from a backwater literal peasant kingdom to a space faring modern country within a single generation, despite a famine and despite the brutal loss of life in WW2. It's very easy to say the country that sends women to school to become nuclear engineers is not as brutally oppressive as the country with a monarch that forcefully sends women to become nuns. How do you determine oppression? Go look at things like literacy, child mortality, education, home ownership, access to clean water, and what kind of occupations women have. By those metrics, socialist revolutions typically and vastly reduce oppression.

Some have, yes, but of the ones I listed, absolutely not.

Revolution isn't an action, it's a consequence of failing and unsustainable conditions. You don't do a Revolution, it happens and you can participate in it.

I think you are vastly underestimating the horrors of most pre-revolutionary societies, and probably also overestimating what you describe as oppression in post-revoltionary governments.

On the first point, here's an excerpt from a JFK speech where he describes pre-revolution Cuba:

The third, and perhaps most disastrous of our failures, was the decision to give stature and support to one of the most bloody and repressive dictatorships in the long history of Latin American repression. Fulgencio Batista murdered 20,000 Cubans in seven years - a greater proportion of the Cuban population than the proportion of Americans who died in both World Wars, and he turned Democratic Cuba into a complete police state - destroying every individual liberty.

And JFK was no friend of Castro; he greenlit the Bay of Pigs invasion! Revolutions are born from the most brutal forms of exploitation and violence. Not even the wildest anticommunist propaganda about post-revolution Cuba comes close to the reality of what the revolution replaced.