I read somewhere that the oil sands are the single largest source of air pollution on earth,
NASA says that the pollution caused by the oil sands is comparable to a large sized coal fired generating plant or a moderate sized city. There are 600 coal-fired generating plants in the US alone
While it is true that producing oil sands oil causes a bigger footprint than drilling for conventional oil, it can also be transported in a much safer and less "impact-ful" manner through pipeline rather than the Exxon Valdez
The method of production is all pretty irrelevant on a global environmental scale: the real pollution comes when this oil (be it Alberta Oil Sands or Saudi Crude) is burned, not produced. There is no such thing as dirty oil or clean oil, there is only easy oil or expensive oil. It is all dirty.
The sad truth is that while we'd all love to have a convenient target like Big Oil or Mining companies to blame for our environmental woes, it is all a lie. We're the ones who burn the oil, we're the plastic consumers, we're the throw-away generation. If we didn't buy, Big Oil would be out of business. If we didn't want new cellphones or I-pads every few months, then cooper and gold mining demand would moderate.