This whole issue isn't debatable and it isn't difficult. Most marinas have a hazardous waste disposal tank. Pumping oily bilge water over board because you think someone else might be doing it and getting away with it, or dumping oil on asphalt is ok because it's a petroleum product is simply lame rationalization. Two wrongs don't make a right. Two wrights made a plane... that sort of thing. Chose the side of caution on this one even if you think "it isn't that much, is it?". It's just not that difficult to do the right thing.
Damn, I never should have posted to this thread.
FOR THE RECORD: I NEVER SUGGESTED POURING OUT OILY WATER ANYWHERE.
I suggested removing the oil from the water and then pouring out the water. Please don't twist what I said.