I'm going to leave aside your points about seaweed evolution and iguana evolution because they are definitely correct and would lead to the collapse of the syst

I'm going to leave aside your points about seaweed evolution and iguana evolution because they are definitely correct and would lead to the collapse of the system I described. Externalities are a real beast! Hehe, well, if humans were able to survive off of sunlight alone, then the only reason to kill something would be "for fun", or in other words, the result of what we would call a mental illness. I wonder if there has ever been an Galapagos iguana vs Galapagos iguana murder. I don't even think they possess the physical capability to murder each other, like, their mouths and hands don't generate enough energy to pierce skin or constrict blood flow or deliver blunt force trauma. If iguanas were able to survive on sunlight alone, eventually they would hit carrying capacity of the place in which they live.