One thing that many green energy advocates fail to understand is the very scale of US energy demand in relation to the output of various green sources.
Let's consider wind.
The Keystone XL pipeline would have provided 900,000 barrels of oil per day, roughly equivalent to 1.53 billion kw-hr per day. A typical wind turbine is 2MW nameplate capacity, but at best actually produces about 30% of this on average. This means that in a day it produces 2,000*.3*24 = 14,400 kw-hr of electricity. This means that the Keystone XL pipeline would have transported an amount of energy to the US equal to the output of 106,250 of those big utility-size wind turbines.
Looked at another way, the entire annual output of the US wind energy sector was about 75 terra-watt-hours per year or about 260 million kw-hr per day. This means that the Keystone XL pipeline would have carried energy equal to over 5 times the total output of wind power in the US.
Of course, this is just based on the potential energy in the fuel, and actual electricity production would be 50-65% less. But even so, this one single pipeline, out of many, is several times larger than the entire wind power sector.