It fossilizes a framework of copyright laws that was created before the Internet. Each country that signs ACTA commits itself to preserving the existing system of intellectual property protection, which many consider to be antiquated and out of touch with the digital world. It ensures that no alternative ideas for managing intellectual property will arise in those countries, which is of course the goal of the United States government and the rightsholders that lobbied for this treaty.
In addition to limiting the flexibility of individual countries without giving them anything in return (other than a pat on the back from Uncle Sam), ACTA contains a number of vague provisions that could lead to more stringent IP regulations. For example:
"ordering the alleged infringer (...) to provide information on any persons (...) involved in any aspect of the infringement" (notice the broad scope)
"endeavoring to promote cooperative efforts within the business community to effectively address trademark and copyright or related rights infringement" ("encouraging" ISPs to "voluntarily" cut off users?).
ACTA also contains provisions that go beyond what is currently law in many of the countries that are about to sign it. For example, it introduces broader anti-circumvention laws that are currently in effect in Poland. It also provides that prosecutors must be able to act out of their own initiative (ex officio) on copyright cases -- even if the rightsholder does not complain.
