The speaker pictures their own mind as a battlefield after the fighting is over. The "multitude" in their head, a crowd of voices, selves, or ideas, now lies dead. Each one has a flag "standing by him," like a soldier whose banner is planted beside his body. The image is quiet and strangely tidy: no noise of combat, just the aftermath.
The title, "Mind crime," suggests that something wrong has been done, and the poem leaves open who did it. Judging by the imagery, the speaker may be the culprit, having silenced all those competing beliefs and loyalties, or may simply be surveying the loss. Either way, the flags hint that each part of the mind once stood for a cause of its own.
The mood is stark, hushed, and a little chilling. The short lines feel like a report from the scene. There is grief here, but also a numbness, as if the speaker can only look and describe. What remains is silence where a crowd used to be.