The phrase "am on side" indicates agreement or support for something, so antonyms for this phrase would involve disagreement or opposition. Some potential antonyms for "am on side" could include phrases like "am against it," "do not support it," "am opposed," or "am not in agreement." These phrases suggest different degrees of disagreement, with some indicating a strong stance against something and others indicating a more neutral or passive lack of support. In general, antonyms for "am on side" reflect a sense of division or disagreement, indicating a lack of shared beliefs or priorities between different individuals or groups.