Atheists cannot believe in a moral design, because they do not believe in a 'designer'. Therefore, on what basis do they judge what is right/wrong or good/evil?
Theists on the other hand, do believe in a moral design. Evil can be viewed as a departure from the way 'things' ought to be. Hence, if there is a way 'things' ought to be, then this implies a moral design.
I think we can all agree that evil certainly exists, which points to a moral design.