This was actually the argument of the governments of Canada, to build it, but add a carbon tax. Canada now has a federal carbon tax, BC has a carbon tax and Al

This was actually the argument of the governments of Canada, to build it, but add a carbon tax. Canada now has a federal carbon tax, BC has a carbon tax and Alberta did have one, but the previous government was thrown out in favour of a deeply conservative one (that is now woefully unpopular so the pro-carbon tax party is probably coming back). You can see one possible issue with the case of the Albertan government changing. Easy to add/remove taxes, hard to add/remove pipelines. There's also even some question of whether the carbon tax will be effective. It arguably hasn't done that much in BC. This is probably because for political reasons it has been set low. A previous conservative government "froze" the tax at low rates. Scientists note the tax needs to be literally $100s more per ton of CO2 to be effective. In my experience the carbon tax has seemed like a good idea, but has seemed in practice more of a political tool to generate the public acceptance of pipelines. The actual CO2 impact of the pipeline is absolutely in zero way mitigated by the carbon tax.