Drinkable water and exporting oil aren't mutually exclusive. To say they are is the definition of hyperbole.

Greater good as in the economic well being of an entire industry vs a fraction of people in a small city in BC with a NIMBY attitude, despite pipeline being the safest way to move oil.  
Another example would be like a neighborhood protesting a new highway being built near them. A whole city benefits so a vocal minority shouldn't be able to veto the whole project.  The only difference is that a highway is guaranteed to produce noise and danger whereas you won't see a pipeline or hear it, but there's a chance of a spill.

If the goal was zero impact, nothing would ever get done. No roads, power lines, water lines, houses, airports, railroads etc. nothing.