The people lamenting “the ruination of the planet” would be the first to be eaten by the people starving due to cessation of petroleum use.

Nobody is advocating for a sudden "cessation of petroleum use". Taking away subsidies from petroleum companies that already make record profits year after year isn't going to cause mass cannibalism, and I'm not sure why you would think that. Replacing petroleum use with sustainable green alternatives also won't cause mass cannibalism - because the energy sources will be replaced with better alternatives. I'm not sure how you jump from "replace petroleum" to "mass cannibalism", it's really quite absurd.