I understand you frustration but the DM pusishing by witholding xp is not going to resolve anything the players should resolve the issue, either in character or out. The DM can voice an opinion but in that case it just another opinion.I can't count how many I've been in the middle of a negotiation, with the support of the majority of the party, only to have one player screw us over by starting a battle. It doesn't matter which way it swings, to a fight or away from one, it's selfish when one person derails the situation for everyone else.