I agree with you that nobody deserves a mind-fucking for doing the right thing.
If BG intends to go see his Mom, I support that decision. However, he should have a ready-made list of non-confrontational responses for Mommy Dearest when she starts handing out the guilt. Moreover, he should be prepared to scram as soon as she makes it clear she is not interested in enjoying the visit.
"You're not enjoying your day Mom. That saddens that we cannot enjoy our time together today. I'll go now. Happy Mother's Day." Perfunctory peck on the cheek. Then get in the car and drive, preferably to a old friend's house who has a fat blunt and a six pack of cold beer waiting.