As has been stated many times before, there are four issues with oil:
1.) Strategic access. Oil needs to be sourced locally so that we can avoid the strategic weakness and enviromental risks of transporting it physically half way across the world. This has nothing to do with the cost we pay for it, but the security of our particular portion of the supply.
As an added benefit, not having to worry so much about securing that supply gives us cost savings in other areas such as diplomatic relationships and military presence.
There is no rational arguement against either of these. Pipelines are immeasurable more controlable and enviromentally safer than tankers. Obviously a source from a friendly contigious military ally wiht most of the infrastructure being inside your own country is a boon to strategic security.
2.) Reducing oil usage altogether. This plays to both the security and the enviromental angle, as obviously you don't need to secure oil you don't use and oil you don't use can't hurt the enviroment.
3.) Pollution in general. The furthur away your physical supply comes from the higher the chance of enviromental disaster related to its movement. You can reduce this risk by reducing the oil you move, or limiting the amount or transport the oil you do use requires.
4.) Global Warming. The transport of oil actually uses up a lot of that oil, so local sources do help with this, but for the most part only squitching to alternatives helps this.
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As I have stated many times before there is no portion of the above that does not fit into some portion of every maintsteam program. If you care less about the enviroment but do about the economy and security, 1-3 still work for you and will help to accomplish 4 tangentally. If you care less about security and are an eco nazi 2-4 appeal to you and will accomplish 1 tangentally.
Again there is no logical reason to not want this pipeline. Is it a pancea for jobs? Nope. Will it still create a lot and help a good deal? Yep. Will it help the enviroment? Yep, the dangers or transportation are clearly illustrated nearly every enviromental incident involving oil. Less transport by less complex means = less enviromental incidents.
As for those saying we are just feeding the addiction, this is a moot point. All else being equal as far as demad goes, local supply is still the better enviromental option over long distance sourced supply. Even if we cut our oil usage in half, the US would still consume the oil supplied by Canada and then some, so the switching to Canadian sourced oil to for the oil we still use in such a scenario is still the smart move.
And of course insinuations that we just switch to solar or wind instead of investing in our current power sources continue to be wishful thinking in the short term. You are basically just appealing to magic.