I presume that you are arguing that if there is no afterlife then nobody has any reason to behave ethically because there is no consequences beyond death.
Atheists have plenty of reason to behave ethically. There is the now and the future until death. There is the fact that most people just want to do want is right because it makes them feel better and that they just simply believe that it right to behave that way.
If the only reason for someone to behave ethically is fear of consequences in the afterlife, then I have no desire to associate with those people. What if somehow in the future you were convinced that there is no God and no afterlife, would you really behave differently to the way you do now?
