In the world at large, people are rewarded or punished in ways that are often utterly random. In the garden, cause and effect, labor and reward, are re-coupled. Gardening makes sense in a senseless world. By extension, then, the more gardens in the world, the more justice, the more sense is created.
Gardening is not trivial. If you believe that it is, closely examine why you feel that way. You may discover that this attitude has been forced upon you by mass media and the crass culture it creates and maintains. The fact is, gardening is just the opposite - it is, or should be, a central, basic expression of human life.