One gets an interesting response when the subject of the Keystone XL pipeline is brought-up in the presence of a "progressive". Sometimes they give real reasons to be against it but mostly they try to change the subject. I think that on some level they know that there isn't a rational reason for opposition. Based on the reasons they give, one hopes that they really don't think these things are convincing:
"Oil from tar sands is much worse for the environment than conventional oil" Okay, granted. But do you think the lack of a pipeline will cause the Canadians to just leave the stuff in the ground? This is usually where they try to change the subject. Oil sells for somewhere in the neighborhood of $100/bbl and it costs less than $40/bbl to produce from tar sands--anyone can do the math. If anything, it will get cheaper to produce going forward. Technology constantly improves and natural gas, which is a major input, has just gotten a lot cheaper.
The alternative to the pipeline is that we will buy more oil from overseas, which will come by tanker. The Canadians meanwhile will pipe it to the Pacific, then put it on a tanker to China. All in all, energy will be wasted.
Yet, I do understand the opposition: Imagine a scenario where North of us was not friendly, democratic and (just as, if not more) environmentally conscious Canada, but rather a country like North Korea. They care nothing for the environment, their people are essentially slaves and all the money will be used to build weapons to threaten us. If that were the case, I would be against the pipeline too.
The difference here is what it takes to elicit moral outrage. What is odd is that the left frequently accuses the right of trying to impose their morality on all of us. They don't seem to notice that much of what they are for boils down to imposing
their morality on us. And the Canadians.