What are the stated goals of the proponents of ACTA? In what way do these goals diverge from the likely effects of the Agreement claimed by those who oppose it?
Regarding purpose, from Wikipedia (emphasis is mine):
The Anti-Counterfeiting Trade Agreement (ACTA) was a proposed multinational treaty for the purpose of establishing international standards for intellectual property rights enforcement. The agreement aims to establish an international legal framework for targeting counterfeit goods, generic medicines and copyright infringement on the Internet, and would create a new governing body outside existing forums [...].
Some of the criticism, also from Wikipedia:
Threats to freedom and human rights
An open letter signed by many organizations [...] states that "the current draft of ACTA would profoundly restrict the fundamental rights and freedoms of European citizens, most notably the freedom of expression and communication privacy."
and (from the same Wikipedia link)
Criminalising generic medicine
According to French EP member Kader Arif, "The problem with ACTA is that, by focusing on the fight against violation of intellectual property rights in general, it treats a generic drug just as a counterfeited drug. This means the patent holder can stop the shipping of the drugs to a developing country, seize the cargo and even order the destruction of the drugs as a preventive measure."