Wikipedia explains Stockholm syndrome as "a condition
which causes hostages to develop a psychological alliance with their captors during captivity". (We can forgive
that this is a sloppy definition because Stockholm syndrome refers to the phenomenon, not the cause of it.)
The force that counteracts this is called "Reactance bias". (You know something's wrong with the people who name these things when they give unrelated names to opposite forces.) Due to the existence of emotions like empowerment, we also are disposed to resist control. But when effective resistance is impossible, it falls solely on one's ideals to resist succumbing to Stockholm syndrome to avoid suffering. The moral value of purity is the impetus to resist. Since all moral truth is necessarily inscribed in all conscious minds, everyone is drawn to uphold Purity by their conscience. The emotional factor of self-esteem is also an invaluable ally here. But since most people outwardly disavow that Purity has any moral value, that impetus is weak, and if subjugated, most people will come to enjoy their subjugation.
Stockholm syndrome isn't a "condition": it's an inherent consequence of human nature. Reactance bias can manifest in misguided ways, but on the whole it's the healthy force counteracting one of the most sinister evils of our nature.