Here's a well written article by Conor Friedersdorf in The Atlantic. Of course, it's tongue in cheek. But listen to the serious argument by an attorney who represented Homeland Security, and a response by Freedom of Press Foundation:

"You can't debate our intelligence capabilities and how to control them in the public without disclosing all of the things that you're discussing to the very people you're trying to gather intelligence about," he said. "Your targets are listening to the debates." In fact, he continued, they're listening particularly closely. For that reason, publicly debating intelligence techniques, targets and limits is foolish. As soon as targets figure out the limits of what authorities can touch, they'll change their tactics accordingly. In his view, limits should be set in secret. A class of overseers with security clearances can make the necessary judgment calls. Trevor Timm, co-founder of the Freedom of the Press Foundation, attempted to defend normal democratic debate. "What separates us from countries like Russia and China is that we can have these types of debates with an informed public that are completely aware of what types of surveillance are available to governments and what the legal standards are," he argued. "We're not specifically debating who the NSA is going to spy on, but whole surveillance regimes. If we didn't debate that in this country, the Fourth Amendment would be classified. But it's not."