How do you know that the website you are on is really the web site you believe you are on? If the DNS record were hacked or changed by a record from another source … SOPA/PIPA bills require the local IP to block or change these records. Then you would not be on the correct site. SSL connections and encryption depend on correct records. These are important issues because considerable amount of money transactions flow through the internet as well as private information.
DNS blocking or denial of service is not a technology built into the internet. In order for local IP to block a site which is hosted outside of the US they must hack the DNS record. This makes DNS hacking a none security threat, or main streams broken DNS records.
This policy is essentially putting MPAA interests above the interests of people who want to have DNS security to insure that they send their information to the correct destination. It effectively gives those who would violate copyrights and hack sites a new tool.
Does DNS blocking prevent piracy. No, all windows systems provide for a local on machine DNS lookup (via hosts file) so they can support an office intranet without needing any new software. The piracy sites can be accessed directly or by adding the DNS lookup to the local operating system.
DNS hacking fails to fix the problem of piracy and makes determining if you are really on the correct site more difficult.