This is the best reason for the existence of God you can come up with? Many types of butterflies bury their eggs inside other creatures, and when hatched the larva eat their host. These relationships were developed over millions of years as opposed to the discussion on God, which has only been going on for thousands of years. I think it comes down to human pride and pompousness to think that we were the reason that matter was brought into existence. Maybe the same reason adopted children need to seek out their biological parents or why we worship historical figures – it gives us a sense of reason for being or makes us feel we are a part of a linear progression that we are the apex of. If we can believe that God is eternal and has always existed, which is mind-blowing, then it is an easier concept to believe that we are an after-effect of billions of years of cosmic evolution.