The antonyms for the phrase "am on one side" are "am on both sides" or "am neutral." To be on both sides means that a person is fair, impartial or willing to consider all aspects of an issue. This is commonly used in legal and political terms where neutrality and balance are important. On the other hand, being neutral means that one is not taking any particular side and remains unaffected by the situation at hand. These two antonyms can be used in the context of debates, discussions, negotiations, and mediation where the goal is to come up with a mutually beneficial solution for all parties involved.