The phrase "are on one side" implies a sense of agreement or unity, but antonyms suggest division and disagreement. Opposing terms like "are on opposite sides," "are divided," or "are in conflict" convey a sense of tension and disagreement between groups or individuals. Alternatively, a more neutral antonym could be "are neutral," suggesting that neither side has been chosen in a debate or conflict. All of these antonyms show that what was once a unified group is now divided or in disagreement, leading to potential conflict or difficulties in decision-making.