Recently I made an oblique allusion (last line of this item) to an article by Eugene Volokh, of UCLA Law School, in defense of "slippery slope" reasoning.
Apparently it was a little too oblique, so in response to a number of queries let me come right out and say: Eugene Volokh has written in defense of "slippery slope" reasoning here, in a Legal Affairs article with David Newman from 2003, and here or here, in versions of a Harvard Law Review article that same year. I think these pieces do a reasonable job of showing why the slippery slope may be useful as a legal concept, whether or not the phenomenon exists in the natural world.* (Sort of like the legal concept of the "reasonable man." Never mind, just a little joke.) Stay tuned for more reader nominees for most plausible real-world example.
And while we're on the legal-concept theme -- ie, slippery slope as a rhetorical device, not a reality -- here's another related entry:
"I think there are some good uses of slippery slope arguments. One example is the general constitutional idea of safe harbor, which I became acquainted with while reading the transcripts and decision in Reno v ACLU, where it became clear that the law was written in such a way that there were large number of sites which would not be considered to be pornographic under the normal understanding of pornography but which the statue would allow to be prosecuted. The prosecution (in Reno vs ACLU) essentially argued, "Oh, we don't intend to prosecute those cases" and the court in effect said, but the law doesn't allow anyone to be sure they are doing the right thing."
Back to the search for real-world examples soon.
* Volokh unfortunately lards his argument with specious boiled-frog references, but at least in the Harvard Law Review version he redeems himself by admitting -- as Paul Krugman recently did -- that he's referring only to fictional figure-of-speech frogs, since real ones would probably try to save themselves.