Relative morality doesn't require a belief in God, but absolute morality (that which would appear to be naturally present, ie: not to murder, steal, etc.) needs to stem from some source. If we soley evolved from inanimate matter, it would be as big a stretch of credibility to believe that people automatically evolved morals that are, for the most part, basic to all cultures, as is believing an intelligent designer put those morals in place.
The big mistake Theists make, is assuming that Atheists are immoral people. There are as many immoral Theists as there are Atheists...and as many moral people of both sides...the real question lies in where the absolute moral guidelines came from. We all can create relative morality to suit our needs...even serial killers can rationalize their actions, though most know what they are doing is "morally" wrong.
My parents contributed 100% of my DNA...if they were perfect citizens, it is still up to me to choose my own path of morality. I won't automatically become a stellar citizen...I could choose to be a criminal. I believe we all have that choice despite knowing what morals we were imprinted with by our parents.
I personally think the argument for absolute morals via an intelligent designer is more plausible than a chance convergence of do's and don'ts across cultures.
Don't know if that makes sense, but in my weakened state of having a cold, it's the best I could do!!