metabolism - How does it make thermodynamic sense for photosynthesizers to turn CO₂ into O₂?

My understanding is that animal metabolism consists of exothermic reactions like

$$\ce{C6H12O6 + 6 O2 ->6 CO2 + 6 H2O + energy}$$

This makes thermodynamic sense to me. Animals need an exothermic reaction to produce the energy we need to move around, etc. However, the other half of the picture, plants and other photosynthesizers producing oxygen, has never made complete sense to me. Are plants consuming $\ce{CO2}$, a "low energy" (I think) substance, and producing higher energy $\ce{O2}$ as a waste product? Is there so much energy available for photosynthesis that plants can afford to waste some of it producing $\ce{O2}$ simply to have enough carbon atoms to store energy via sugars?