The whole idea behind the Natural Born Citizen rule is that we want a president who is 100% loyal to this country and no other. We see Obama's policies, which hurt us, hurt our allies, and help our enemies, and we see his questionable eligibility, and we see a link between the two. The policies and the legitimacy are the same thing.
Our founders were pretty smart guys, but I wish they could have envisioned some of the distortions the left has championed and but in some more distinct wording; Natural Born Citizen - Prove it with signed documents from witnesses of the birth, Abortion - Define when life and rights begin, Separation of Church and State - Just ban satanism, islam, and tell atheist they have the right to keep their opinions to themselves, Birth right Citizenship - I wish they had seen the problem we are having with that one, Protecting our borders with the best available technology available, etc.
Well, then, you can see why democRats oppose this thinking - NONE of them would ever qualify.