Killing all religions will not lead to the destruction of mental illness, because non-believers can also succumb to aggression and violence. It all begins with violence in childhood and from television screens.
Killing all religions will put a stop to the religion based violence, and the exploitation by the clergy. But I agree that it will be having hardly any effect on the other social problems, such as crime and unemployment.
All religions support the myth that God created people different. It is aimed to continue the rich richer and the poor got poorer. States are interested in such an ideology. This helps to keep popular revolt. In our time religion is a part of public policy.