WAGMI expresses collective optimism and belonging. It builds community, and it also functions as group reassurance that suppresses dissent: in a room chanting it, the person with a bear case has to choose between being right and belonging. That is groupthink in four letters.
It is harmless as a joke and worth noticing as a signal. When a community's main output is mutual encouragement about a position everyone already holds, there is no information left in the room.
Related: ngmi, groupthink, echo-chamber, social-proof