but it's also not obvious to me what the environmental effects might be. It's actually a tricky problem. What is the environmental damage if such a pipeline works properly? What is the likelihood of a significant failure? What is the environmental damage if such a failure occurs? Maybe most important, how do those environmental risks compare to those of shipping similar quantities of oil by train or truck?

A lot of people seem to think that if there's no pipeline then it just puts the Canadian tar sands out of business, but that is obviously not the case. Given that this oil will be drilled (or more to the point: given that our need to cut back on fossil fuels, however legitimate it indeed is, is a separate issue), what is the environmentally-optimal course of action? I'm really not sure. And I hope we aren't just taking numbers from advocacy groups. It's not just that people have axes to grind, it's that these calculations really are complex.

For the most part, I assume it's a minor issue either way. It just gives us all a reason to despise one another, which I'm all for.