In a word........ bollox I believe that any two people can make great parents, whether they're natural parents, adoptive parents, gay parents, black, white or purple, as long as they are loving, honest, caring, and provide the child with all the basic principles to be a good person etc and provide them with love and warmth, security and food, clothing etc.
I dont believe anyone should be denied the joy of being a parent and raising someone precious to them. Just my opinion of course.