The combined efficiency of an electric motor + fossil fuel power plant is still much greater than in a conventional internal combustion engine and therefore the environmental impact from the car is much reduced regardless of the fuel source.

A secondary factor - driving a car like a Tesla communicates an image of environmental responsibility. Even if the government and energy companies aren't supporting renewable fuels, you are. When there is a wind turbine on every corner, and a solar panel on every roof, you will be ready with your Tesla. You're a good citizen, and a forward-thinker...