How do weeds help the earth?

Weeds serve as easily established, easily uprooted ground cover. They provide food, and shelter, for wildlife. They hold banks together, against erosion. They grow in poor soil. They give seasonal color and interest. They engage in photosynthesis. So they take in carbon dioxide from, and add oxygen to, the air. They decompose, and add to soil biomass. When weeds protect from erosion, they help the fish.