I think the call for a ban was reflecting the fact that a lot of energy is required to produce usable crude oil from tar sands. It basically involves burning natural gas to produce steam to "melt" the tar sands to be able to flow. This makes the CO2 footprint of tar sands oil significantly higher than standard oil, it would be like powering your car with coal rather than oil. A reasonable CO2 tax would render tar sands uneconomic.