The antonyms for the phrase "marching against" could include "marching for," "supporting," "endorsing," "aiding," "backing," or "upholding." While "marching against" implies a sense of antagonism or opposition, the opposite verbs suggest a more positive or cooperative stance. For example, a group might march in support of a particular cause or candidate, rather than against a rival group or political leader. By focusing on the affirmative values and goals they hope to achieve, rather than simply opposing another group or idea, protesters or activists can build a more constructive and inclusive movement.