Parents have a right to decide.
A fit parent will not normally deprive a child of a healthy relationship with a grandparent, if that is the case. A third party should not have a right to a child they did not bear themselves. Such laws may enable very unhealthy relationships. Even under supervised visitation, I think that this causes more heartache, a parent being forced to give a third party, sometimes an abusive parent, rights to a child they bore. A child they love.