Presumably it's a postulate, and applies in all reasonable cases. The generalization was given as an example of a larger truism.

To give a specific example: Solving discrimination against Maronites by instituting a system of power sharing which discriminated against Shiites and Druze set Lebanon up for failure. Can you think of an instance where reactionary counter-discrimination solved an issue long-term? Why be skeptical of the assertion of "two wrongs don't make a right"? It's generally observable in all cases that retributive "justice" simply creates resentment, deepens issues and erodes belief and trust in social institutions.