Yes, graduated response antipiracy laws can be effectively enforced, because in the modern era, record keeping of activity can be good enough that enforcers can keep track of who has violated what, and how much. It is a fair enforcement system that can be done at a cost that is effective and fair to both producers and to the public.
Yes, graduated response can be effectively enforced, because it is effectively used in some places, such as France. Studies have shown that implementing graduated response results in higher sales, especially in genres that report high piracy rates, such as pop music. When people realize consequences of piracy are severe, they may seek to become legitimate purchases.