That's a gotcha if I've ever seen one. Why would self serving motivations be a disqualifier? Not to mention, you can basically argue that it's always self serving motivations no matter what.
That said, yeah things are more likely to go badly than to go well. Nation building is hard; the allies were able to reform Japan and (West) Germany because while they had evil states, the states were at least functioning. It seems easier to improve governments morally than functionally.
Haiti lost its functional state when the French colonialists fled en masse after the 1804 massacre. Due to racism, they were the only ones allowed in administrative positions in the bureaucracy so when they left Haiti, it was left with no one qualified to run the state apparatus. Since the population were transplanted slaves, they had no tribal traditions to fall back on. Without a continuity of bureaucracy it was left hobbled to this day. Since the state can’t afford to police the population, these gangs fill the void because they can use force to collect taxes (in the broadest sense because usually this takes the form of business shakedowns and roadblocks that they use to extract money from the population).
Of course German elements of democracy goes back to pre-Christian times: https://en.wikipedia.org/wiki/Thing_(assembly)
> The period saw a breakdown in the traditional master-servant relationship between a lord and his vassals, with many instances of vassals rebelling against their lords, internal dynastic conflict over lordships within noble families (in which vassals would take sides), and the installation of figurehead lords by cadet branches of noble families.[3] The period was also marked by the loosening of samurai culture, with people born into other social strata sometimes making a name for themselves as warriors and thus becoming samurai.
> [W]eariness of war, socioeconomic unrest and poor treatment by aristocrats provoked the wrath of the peasant class. Farmers, craftsmen, merchants and even villages would organize uprisings (known as "ikki") against the ruling class. An extraordinary example is the Kaga Rebellion, in which the local ikki had staged a large-scale revolt with the support of the True Pure Land sect (thereby establishing the term ikkō ikki) and assumed control of the entire province of Kaga.
Whatever post-Heian, pre-Meiji Japan was, it was not an orderly, harmonious society.
[1]: https://en.wikipedia.org/wiki/Abolition_of_the_han_system
Contrast that with Haiti where the vast majority of Haitians weren’t allowed to hold administrative positions in the colonial government so when the remnants of the French bureaucrats fled after the 1804 massacre, Haiti was left with very few people who knew how to run any part of the government. They were left with post offices but without anyone with the experience to actually run a postal system. No officers capable of training and disciplining a police force or military. And so on. They had to build up their bureaucracy entirely from scratch which is an incredibly hard thing to do and usually turns into situations like in Haiti, as opposed to outcomes like Japan where the state isn’t violently wiped clean. It’s hard to overstate how big a roll that continuity plays when a new polity forms in its success or failure.
A sibling comment mentioned the Australian intervention in East Timor. I can easily dismiss that by saying “well the Australians have a vested interest in a stable neighbourhood. They’re just self pricks looking out for themselves”. This statement would be technically correct but also pretty meaningless in this discussion.
The Caribbean is a special case though where there are lots of miraculous turnarounds because tourism is so lucrative.
The West supported an brutal military dictatorship in South Korea for decades. South Korean democracy is the result of internal struggle by the South Korean people.
I mean, the US was a huge supporter of Suharto in Indonesia as the "less bad" option to the thread of communism, and Mubarak in Egypt as an alternative to the worse option of a Islamic Brotherhood run state, or possibly something even more deeply Soviet aligned. I don't think there is any "lesser evil" warlord to pick in Haiti right now and prop up above any of the others.
If you're just intervening because you're charitable and nice, then things will be mismanaged and messed up.
Like the UN peacekeepers raping and spreading cholera in Haiti.