Stopping a pointless battle to allow your son to attend his scouting function has zero to do with absolving XW of anything. Not playing her game and feeling "forced" onto the defensive is simply the better move. Ever seen War Games? Continuing to engage XW in such battles costs your son. If she isn't doing something legally actionable and she is doing something within the context of your agreement (having custody of son and not sharing it on her day), then fighting about it isn't going to go anywhere except making co-parenting harder, which is harder on your son.
Have you tried no contact except for email? Email makes it easier to keep things strictly business. It helps avoid those landmines that WASs often seem to scatter so prolifically.
