It can't be undone.

[To him, that's not an argument against any of what's been said here so much as a statement of fact.]

I don't know whether you knowing changes anything. I wouldn't have expected the Luke I knew to do what he did, either.

[He's very sure the Luke who practically raised him from the time he was ten and taught him and the other students how to be Jedi would not have advocated attacking a relative in their sleep. And yet.]