Read the rest of this thread. Burning plastic for energy reduces the need for oil from the ground. It's by far the best way to handle plastic.
It removes waste, it's emits less CO2 than pull extra oil from the ground, and it's cheap. You don't get a triple win like this very often when it comes to the environment.
His point might be that the carbon in the plastic will some day be released to the atmosphere, either through decay, combustion, or even digestion. Might as well burn it now and recover some energy in the form of heat from it.
It removes waste, it's emits less CO2 than pull extra oil from the ground, and it's cheap. You don't get a triple win like this very often when it comes to the environment.