They simply had a different personal preference than you do. The point is, you shouldn't tell anyone that they are wrong or even right because they aren't either of those things. You can believe that its wrong, but you have no place to ground it. People can do anything they want to do without getting punished for their actions if the world lived consistently with the belief that God doesn't exist. There is no purpose to life.
Life has no ultimate goal.
There is no reason for living. Sacrifice for someone else's life would be stupid. This argument shows that an atheist lives inconsistently with their own belief. If you said no, that he isn't doing any thing wrong, then you would be living consistantly with your beliefs. But if you said yes, then you would live as if there were objective morals.