Peter R made the case against handwashing on errtravel.com.
“Let’s assume you wash up before leaving your hotel room. Consider the germs, dirt, cleaning product residues, and other contaminants you probably picked up on your way out of the hotel, getting into and out of the taxi, paying the driver with cash, taking your shoes off and putting them back on at the security checkpoint, eating at the airport restaurant, shaking hands with colleagues going off to other flights, and so on. (And then consider the germs you pick up if you happen to rub your eyes, touch your hair, blow your nose, scratch your arm or leg, etc. during this time.)
Now you enter an airport restroom, where there’s often no door to touch and with urinals that automatically flush. You touch your clothing (pretty clean) and one part of your body (pretty clean, assuming good hygiene). (Plus note that urine is generally considered to be sterile.) And NOW you’re worried about what’s on your hands? I’d suggest that most times, your hands are not measurably dirtier when you leave the restroom, than when you entered.
In fact, it would probably be better if men washed their hands when ENTERING the restroom, so they don’t expose a sensitive part of the body to all the stuff they’ve picked up in getting there!”