Since all humans are fallible, we need to limit their opportunity to screw things up.  Once the pipeline is in the ground, it's a lot harder to screw up than a huge supertanker moving crude from Mexico or Venezuela or a 100 car train running down the Gorge than a pipeline in a wheat field in Nebraska somewhere.   A screw up there is multiple risk factors safer to people or the environment than the other options.

The oil will be moved.  The oil is not going to quit being moved unless it is forbidden by the government or uneconomical.  Those things may happen someday.  For the foreseeable future (25-50 years) the oil is going to be moved, refined, and used around the world.