God or accident are not the only possiblle alternatives. If they were, then whatever exists would exist by accident; either the the universe would exist by accidenct or God would exist by accident. Most theist have trouble saying God is an accident, but, if God does not have cause, what do you call it?
Accident is the only natural explantion (and frankly its not rational.) Everything else implies a violation of natural laws i.e. the supernatural. The debate then becomes one about the nature of God.
if God does not have cause, what do you call it?
The limit to reason :-)