I think comparing previous abuse to marriage isn't that useful, as that is an instance of previous consent not justifing future consent not, previous abuse of consent leading to not being able to understand or recognise consent.
If CWC is following the rules for consent taught to him and practiced upon him by Barb, isn't it possible that he doesn't properly understand what consent is (in the same way we all do) in his interactions with Barb?
Like
@Fareal said in another post, anything and everything that can be used as a mitigating factor in sentencing will be. Defense attorneys will argue that a defendant's difficult upbringing, abusive childhood, emotional immaturity are all reasons a sentence should be mitigated. That rarely works when you’re talking about someone who is being accused of raping their elderly mother, of whom they also act as a caretaker for.
What you are proposing, which is even
theoretically extremely unlikely, would require Chris's attorneys to argue that Barb has been molesting and/or raping her adult son for decades and that Chris has been the victim of that crime. Those types of defenses are extremely unlikely to work and I cannot imagine a defense like this even being attempted in a non-murder case.
This has the potential to be a rape charge (right now, it is incest which appears to be able to be a misdemeanor or a felony and would almost certainly be pled down as
@Alexander Hamilton said in his first post), which is definitely serious, but you don’t go for the “my mother was actually the one who had been raping and molest me for years“ defense for something that will almost certainly be pled down to a felony plea, a suspended sentence, and requirement to register as a sex offender.
Also, PD's are way too overworked to give this type of thing that kind of attention. Jose Baez is not going to represent Chris. Maybe if Chris killed Barb, that sort of defense theory would make more sense. But even then, Jose Baez, is not going to be Chris's lawyer.