The standard pillars of the Imperium of Man stand as Purge the xenos/burn the heretic/kill the mutant. So obviously they violently oppose all mutant races, heretics and aliens. But the Ogryn are described as being a mutant/differently evolved subspecies of human.
Why are Ogryn the exception? Why are they allowed into the Imperial Guard and even at time allowed to be squad leaders?
'Blessed is the mind closed to doubt' may apply, as they are too dumb to question most things, but they have shown an equal tendency to be corrupted by Chaos as regular Imperial Guard, so this is not a significant enough advantage.
Is there any lore that explains why they were even given a chance and not outright exterminated?