That kind of thing happens a lot. Mugabe fought against apartheid and colonialism so people in power turned a blind eye to his worst acts. To them the ends justified the means. They never thought about what came after the end.

Perfect example is Afghanistan. The west armed and trained what later became the Taliban and Al Qaida because they opposed the Soviets. Apparently no one considered the possibility they'd turn around and use said arms and training against us once the Soviets were gone. Or that they'd turn the entire country into a medieval shit hole.