It's called moral licensing:
We drink Diet Coke -- with Quarter Pounders and fries at McDonald's. We go to the gym -- and ride the elevator to the second floor. We install tankless water heaters -- then take longer showers. We drive SUVs to see Al Gore's speeches on global warming.
.... It seems that we have a good/bad balance sheet in our heads that we're probably not even aware of. For many people, doing good makes it easier -- and often more likely -- to do bad. It works in reverse, too: Do bad, then do good.
"We have these internal negotiations going in our heads all day, even if we don't know it," said Benoît Monin, a social psychologist who studies moral licensing at Stanford University. "People's past behavior literally gives them license to do that next thing, which might not be good."
The implications of moral licensing are vast, stretching beyond consumer decisions and into politics and environmental policy. Monin published a study showing that voters given an opportunity to endorse Barack Obama for president were more likely to later favor white people for job openings.Read it all.
The survey is now closed. [July 30]
Results are discussed here.