Arguments against organic agriculture rooted (ha!) based on the belief that the efficient practice of organic agriculture requires tilling, with resulting loss of topsoil, don't hold so much weight as they once did. The Rodale Institute, which is a sponsor of organic agricultural practices, has information on organic farming that adopts no-till mechanical practices, albeit with adjustments made in order to adhere to organic standards:
http://www.newfarm.org/depts/notill/index.shtml
Obviously, if you read the FAQ, there are certain stipulations to no-till organic farming, but it's interesting to see that it is in practice.
One thing that's bothered me about the conventional/organic ag. debate is the fact that many arguments on each side of the debate are motivated by outdated modes of thinking and old data. Everyone gets all bent out of shape, because, well, people care about their food and the food supply.
I was reading stuff on the Heartland Institute's website (which is a conservative-leaning clearinghouse for skeptical inquiry into science and public policy) this morning, just for kicks, and came across this paper called "Organic Food is Not Better for You."
Link:
http://www.heartland.org/Article.cfm?artId=21608
The major fallacy of the paper was its use of sources from over 30 years ago in order to support its claim that organic food is fool's gold. And by using such information, from only a few sources, I really can't give that thesis' claim much credit. Of course, Heartland's got their own agenda to sell (so too the authors of that paper), but any researcher with any sense is going to look at that page and laugh.
I know that there are better sourced and written arguments against organic ag. out there – but I'm just surprised to see that a group that holds so much sway over public policy has done such a lousy job of proving its point.