At first glance, the argument seems compelling--but how significant is the impact? In "Economic Sanctions: Public Goals and Private Compensation," found in the Fall 2003 issue of the Chicago Journal of International Law, Gary Hufbauer and Barbara Oegg analyze the economic effects of sanctions.
First, the impacts on trade are relatively small:
Over the past decade, the emergence of new senders such as the European Union and the United Nations, coupled with an expanding list of foreign policy goals, has lead [sic] to a proliferation of new sanctions initiatives. Despite these developments, the total amount of trade disrupted by sanctions remains relatively small. Our estimates indicate that US trade loss due to extensive sanctions ranged from 0.7 percent to 1.8 percent of total US merchandise trade. Lost EU trade is probably much smaller. Similarly, average annual costs of economic sanctions to the target countries seldom exceed 3 percent of GDP. Compared to the tremendous expansion of international trade and capital flows in the last decade, the costs of sanctions in terms of national income or bilateral trade flows seem minor.However, investment impacts are considerably larger; according to Hufbauer and Oegg's calculations, sanctions affect "as much as 10 percent of world [Foreign Direct Investment]," and that this, on average, would decrease target countries' GDP by a "substantial" 6%.
If the economic impacts are mixed, what might represent another approach for the affirmative? First, consider the wording of the resolution--"... to achieve foreign policy objectives," which in most readings applies exclusively to governments. The affirmative might argue that private actors are a more appropriate agent of action--that individuals and corporations, through grassroots direct action, nonviolent revolution, and litigation, can go after rights violators and rogue regimes.
Hufbauer and Oegg note the Free Burma Coalition, which
...claims that it successfully pressured companies such as Eddie Bauer, Columbia Sportswear, Apple Computer, Motorola, Heineken, Eastman Kodak, Amoco, and Pepsi, among others, to withdraw their businesses from Burma. Some 39 major US retailers have also announced their decisions to cut off all business ties with Burma. Grassroots divestment campaigns are not solely a US phenomenon. Under pressure from the Burma Campaign UK, eight UK investment funds launched an initiative highlighting the unique problems for foreign investors in Burma including the threat of international boycotts, corruption, and the loss of shareholder confidence.Hufbauer and Oegg also foresee a future in which private litigation, enabled by legislation such as the FSIA and the Alien Tort Statute, and by courts with growing international reach, put a much larger crimp in the economic style of state sponsors of terrorism.
I'm not sure it's worth building a whole case around, but at least it offers a potential block to Negatives arguing that no realistic peaceful alternatives exist.