Who's to say he wouldn't use it in a villainous context? Just saying.

But after reading and rereading and analyzing the shit out of Sasuke and Madara's interactions for reread_no_jutsu, I have to be devil's advocate and say there is a strong, strong chance that his villain face is just an act to get Madara to think Sasuke's on his side.

Which Madara probably knows, and already has a contingency betrayal plan.

God, I love the Uchiha.