This is a good topic and I'm sure it will get some varied response. Kaerbear your story made me so upset about your sister in law and frankly scares me to death.
My family recently had an upheaval that involved my brother, his wife, my parents and my niece. The fighting went on for months. My sister in law was forbidding my mom to see her grandchild because they were fighting. They were constantly putting my niece in the middle of the arguments and using her as a pawn. They would basically tell my mom that she must see things their way or they couldn't see their grandchild. It was really sad. Eventually they made up and things are back to normal, but it scares me that they might try to do this to my mom again. It absolutely tore my mom to pieces so much that she could barely function.
Several times she talked to lawyers about getting some grandparents rights for visitation. The lawyers told her that if she went through with it, that they would have a good chance at winning, and being able to have some visitation with her grandchild.
I think that under certain situations, that it is good that there are some kind of grandparents rights. If the parents are abusive, un fit, doing drugs, and basically in an unsafe situation, then it is a good thing for the child to be removed. In my family's situation, I think that it would have been good and bad. I do think that my mom has some right to see my niece, but on the other hand, I can only imagine the damage it would cause between my mom and my brother and sister in law. It would have cause some irreversible damage. not to mention confusing the heck out of my niece.