He is the 2nd best player on the team and supposedly not starting is a thing for him and really the 2nd best player usually starts. If for nothing else than to make him happy I would start him. It is not like he doesn't deserve it, production wise. Why alienate the kid if you don't have to? I am not really worried about next year, but by the same token........
1) he doesnt seem to care - certainly isnt reflected in his play
2) there is a long history of sixth men being better than multiple players in the starting five. Waiters for cuse was a good one. Manu Ginobili is another. Jason Terry for the Mavs. Odom for the Lakers. Harden for the Thunder. It's not like this is the most bizarre idea ever. You are right on most things wasju, but dont agree with you here.
3) even if all this is is a punishment, this is much better than reducing his minutes, yanking him around so he doesnt know what to expect, or suspending him, isnt it?