To all of you who replied to my initial post, thank you. I've read all the responses carefully, even the trolls: they too have their story. There's a wealth of excellent advice here and a high signal-to-noise ratio. Thanks in particular to those of you who took the time to provide thoughtful and well-rounded answers. Will this idea fly? Beats me. But I hope to have a lot of fun finding out.

This judgement has no effect on free speech in any case, merely on the right to anonymity, a different question entirely. On the topic of free speech, Oliver Wendell Holmes (an American Supreme Court Judge) put it very well. "The most stringent protection of free speech would not protect a man falsely shouting fire in a theater". Not even in the United States is the right to free speech absolute - nor would any sane person want it to be.

Two important issues: 1. There is nothing illegal about pornography in general. It doesn't matter whether he had two or two million pix of naked women. Their discovery is as irrelevant as wedding photos. 2. Nowadays there are so many ways to carry files around - SD chips, CDs/DVDs, on your iPod, on an encrypted HD partition, not to mention just downloading them later - that this sort of search is largely pointless. Any serious importer of child pornography wouldn't even be inconvenienced by them. This is not to downplay the legitimacy of the child porn issue - but measures like this waste time and effort that could have been used elsewhere. In Bruce Schneier's phrase, security theater.