If you care about the environment, don’t celebrate this action. Valves on pipelines typically aren’t used to throttle flow rate, but to isolate sections of a pipeline during maintenance and repair and for diversion of flow upon multiple line junctions. Viscous crude oil like that from Alberta may use positive displacement style pumps called rotary gear pumps. These pumps aren’t meant to operate routinely with sudden line restriction and pressure build up. While there are automatic shutoffs in the case of pressure build up and instant motor speed changes, shutting off the flow while in operation is simply dangerous. Alberta oil sands has potential to become multiphase flow, where liquid and vapor hydrocarbons begin to separate. That adds to more issues.
Essentially what these activists are doing is making all environmentalists seem like idiots. So all you environmentalists inside Hillary’s circle, like our esteemed environmental NGOs and think tanks, better tell those outside the inner circle to cut crap like this out.