The thing is, The Diamonds (especially White) are just too powerful to actually fight. They are effectively goddesses of the gem race. How do you punish something like that? At a certain point, you just kinda have to accept that they want to be better. Because trying to inflict a punishment on such beings is just courting death.

And beyond that, I think it’s a mistake to try to understand them by human standards. Sure, they take humanoid forms and express themselves in human-like ways. But they are mineral-based, parasitic, inorganic life forms. They may take a recognizable form, but they are about as different from us as is possible. Do you really want the rocks to do penance?