It's a valid question, but consider a counter-example:

It is against the law to drive drunk, because intoxicated drivers are statistically far more likely to be involved in accidents that harm or kill people, or damage property.

However, if I am determined to be drunk driving, I will (and should be) jailed even if I've harmed nobody, because the law exists to mitigate a potential harm.

If I drive drunk and I get off the hook because I'm a celebrity or a government agent, whether or not I cause harm is irrelevant; I broke the law -- thus the argument becomes a "rule of law" issue, which particularly in a Constitution area like search and seizure, is one of the most important areas for the Federal Judicial branch to handle (and I do believe that this will end up before the Supremes, who I think will strike some or all of it down as an un-Constitutional encroachment of Executive power on the Constitution).

In rule of law cases, "harm" isn't necessary. Of course, it can certainly bolster a case to show harm, but as others have pointed out, due to the (intentionally) secretive nature of this issue, it may be hard to show actual harm. A wise judge should realize this, however, and allow some hypotheticals to be used. This is similar to judges putting a hold on an entire state's executions because hypothetically an innocent man might be executed.

The short answer: I doubt anyone can demonstrate harm; not because there's no harm, but because It's a Secret. The longer answer: I don't think that that will matter in the long run.

<soapbox>

The legislature should never have let this pass. Once again we see our Congress abdicating their sworn duty to protect and defend the Constitution from all enemies, foreign and domestic.

</soapbox>