We have chosen not to join.
I'm not sure if AARP has an official policy position on grandparent rights, but after seeing several articles they have published that seem to support it, I cannot give this organization any money.
We are opposed to grandparents rights and unfortunately know what it like to get to the point where you have to sever the grandparent/grandchild relationship for the best interest and safety of your children. I've heard too many stories in my online support group for this issue where sympathetic seeming grandparents manage to get court ordered visitation with their grandkids. Typically the grandparent in question has done decades of abuse to the adult child but is very manipulative and cunning with the court system. I can even imagine a court forcing you to send your child to visit unsupervised with your abuser. It's really sad. Old people tend to vote in greater numbers, so grandparent rights are being expanded in many states.