Grayson lacks vitamins and proteins I guess . Very very very very verrrrrryyyyyy low IQ and common sense. Someone needs to slap some sense to him , I don't know who'll be that person. Dane didn't seem like he has any interest to knock some common sense into Grayson. Joshua would be right , beating the shit outta him if needed .
That's the first problem, no one can directly teach him how to be normal. We see it when Joshua confronts Grayson, he doesn't understand what is wrong about his actions because logically he is doing the right thing even if it hurts others. And we see it when Dane is paid to beat up Grayson, he will respond to violence in kind because it's self defense. And (a tiny spoiler) when Joshua pays to have Grayson kidnapped, Grayson starts acting pitifully to catch Dane off guard and to escape without caring about hurting himself because he needs to escape.
What actually makes Grayson change is coming to care about someone, because it forces him to confront what he should care about. As Grayson gets closer to Dane, he comes to understand that although he may not directly care about what Dane cares about, he should care about what Dane cares about because he (Grayson) cares about Dane. It's like the most roundabout way to learn, but Grayson isn't normal enough to learn from teachers or from being beat up.

I guess everyone forgot that this is Grayson, the same man that told his younger brother that he fucked a dog while in a rut to scare said brother into releasing his pheromones. In Grayson's head he understands things differently, and it's not an excuse because he is a grown ass man, but it really explains why he can't act like a normal human.
Based on the fact that Dane immediately took action to rescue the boy, Grayson has barely understood that what he did was wrong - not on the basis of the principles of morality, but merely as a wrong answer on a test. But to Grayson, if one is being punished they must serve the time even if it's abuse because that's what he grew up with. He doesn't see anything wrong or problematic with the situation but based on Dane's reaction, he understands that he will be scolded for not acting in the right way. Ultimately Grayson is going to be on a journey to learn how to gage emotions and how to properly respond to situations.