As a matter of fact, electric cars would be more efficient than ICE cars even with a very high-carbon electricity mix, because thermal power plants are much more efficient than ICE engines (due to size + available cooling source), and the power transmission/battery/electric engines are optimized enough that they don't gobble all the efficiency gains.

Electric cars are better CO2-wise, no question. But it will not reduce emissions enough. People who can afford not having a car should do so, and public authorities should develop public transportation. Of course, people who can't do so will be better off with an electric car, but environmentalists are worried that a push to full-electric will undermine needed efforts to reshape society towards a less energy-hungry world.