DutchJazzer-- Think you missed the third possibility. Just leave it as is! Just retired from the water reclamation industry and my professional opinion is this - six of one and half a dozen of the other. From a purely environmental viewpoint i think you should become more familiar with chaos theory. You know, the one that states something like "If a guy from Utah washes instead of wipes the global economy collapses".
Now you're polluting the air and that directly affects my nose. Your chaos theory is like the female cycle being responsible for a lot of heat... chaos. If enough people don't wipe you're probably going to cause road rage, nausea induced uncontrollable vomiting, rubbernecking like never before, and the entire system will gridlock. Always wipe, dudes, our auto insurance policies depend on it.