I've actually heard the argument:

Those trucks and trains were already making the trip... Keeping the pipeline would not stop them!

This ignores the simple, grade-school level concept that the vehicles can only carry so much freight per trip. More freight means more trips. Adding the oil that's not being transported by the pipeline means the vehicles have to make more trips than they would otherwise. It's such an elementary concept, it's depressing I have to explain it to grown-ass adults.

It's the same bullshit argument that they use to defend Planned Parenthood receiving federal funds while giving money to Democrat politicians.

They're not using the government money on campaign contributions! That goes into a separate account that only funds operations!

This ignores the fact that the organization has extra money to give to politicians that they could and should be spending on operations instead! To pretend this is anything other than embezzlement of public funds is asinine. Shit like this is the reason the phrase "mental gymnastics" was created.