I made a short post on this on my main blog, but I wanted to note the implications here. My point is that most people project their thoughts and feelings on others. That means that open minded adoptive parents will work with the birth parents, expecting the same thing in return. I would be that most birth parents are quite selfish and would (and will) cheat the adoptive parents as soon as they get the chance, since they expect that the adoptive parents would do the same to them.
Note that this is in spite of anything the adoptive parents do. We drove our three youngest to have a reunion with their birth family while all of them were still minors but this didn't gain us any credit since the birth family figured we were just like them (in their own minds at least) no matter what our outward actions were.
This may differ in adoptions not through the foster care system, but I would venture that most birth parents that are in a position to relinquish or lose the right to parent face similar life challenges.