Your son's behavior is all too familiar...I am sorry to say that even after a year we still have those conversations...
what I am learning (slowly...I am a slooow learner !) is not to participate in the debate....
my husband refers to it as playing verbal ping pong...he starts presenting his opinions and I fall into the trap of discussing and before I know it, it sounds like I've agreed to some but not all of the plan when in reality I am not in favor of any of the plan!
now I try (emphasis on try) to just say no as soon as the twisted thinking starts and refuse to engage in negotiating.....
easier said than done but crucial...
keeping you in my prayers