You are clearly someone who does not like to be told they are doing somehting wrong...sure the water goes rigth back down the drain, but it surely has to be RE-TREATED before it comes out of your pipes again. I would prefer my water only treated once.
Unfortunately, many environmentalists may exaggerate facts & stats, but that is also many times the only way to make a point with some people. If people think "that's not so bad", then they are less likely to change. What would be the harm in turning the water off while brishing your teeth? Do you need that water? We are so used to CONSUMING, that occurs to very few to CONSERVE. Why should we? Because it only makes sense not to waste/use what we do not need. This bleeds right into our reckless spending habits and most of us in terrible debt...unless you think that's an exaggeration, too.