You know, I like to think that the true end goal of Hollow Knight is not to quell the infection or beat the Radiance, but instead to simply release Hollow from their torment. Sealing/getting rid of Radiance is merely the last stepping stone to achieving that goal. Given everything we learn about the siblings it just feels more right that that would be Ghost's true goal, peace for their suffering sibling, in whatever form they can achieve it.
honestly, i always interpreted it that way too - like killing Radiance was a personal revenge, not some kind of noble goal for the good of Hallownest. It’s for Hornet who literally feels like she couldnt leave because she had to guard a shitty ruined shell of a kingdom, and all the people who are endangered by the infection and could be again, and the fact that Radiance puppeted their suffering siblings and prolonged their agony so she could try to kill ghost through them and like
man, no wonder they just beat the shit out of her! they’ve taken all this time to learn the stories of people they care about and all of it is something Radiance could just sweep away in an instant, she’s tortured and wrung life out of their siblings, and it’s not about Hallownest and it never was. It’s just about stopping more suffering and ESPECIALLY hollow’s suffering, the person who was condemned to hold a literal god and have her agonizingly break them open from the inside for probably centuries.
so yeah tl;dr I always thought for ghost murdering Radiance is personal, not because they thought it was the right thing to do or whatever. They just want to stab this fucker in the eye for making them suffer and making their siblings suffer.
