Moral flexibility
Moral flexibility explains why one form of cheating is ok but another is not. In absolute terms they are both cheating, in relative terms they are both different, in reality they are part of the balance.
Tax evasion can be seen as a bad thing (for good reason) yet because people can do so it incentives governments not to rob all of us blind (because those who can move it will and the gov loses). Compare that with the well established morality of music piracy.