So sad that ppl no longer grasp economics, or how things work. It used to be that ppl had enough sense to at least study a bit prior to piping up.
Look, this is already an almost done deal. Assume that it is not. Then what changes? Well, instead, nations like China will continue to get their oil from other locations. Basically, oil demand will NOT go down just because you stop a pipeline. In fact, tar sands will continue until the price hits about 50/bl, which none of the producers will allow directly.
OTOH, If America allows keystone, BUT IN RETURN, insists on limited time subsidies for new commercial vehicles using nat gas, then within 3 years, limiting it to serial hybrids using nat gas, this will drop America's demand for oil. That will spread to other nations as nat. gas vehicles come down in price. And with the serial hybrid commercial trucks, that can not only increase semi vehicles to 50+ MPG from the current 5 mpg, BUT, it will drop oil demand, and its prices.
Look, back in the early 80's, I used to protest against the manufacturing of nuke triggers in Colorado. And it was in fact, shut down AND cleaned up (thank god; it was bad). However, we are now creating a new site in which to make newer better triggers. Nothing really stopped. Now, these are not about economics, but about politics. BUT, oil/nat gas/coal/etc combined with climate change is not really about politics, but economics, combined with some politics.
Here. Read this.