The following is from a Reuters news article. Here's a paragraph from about two-thirds into the article:
The Netherlands, which already has liberal policies on soft drugs, prostitution and gay marriage, was shocked by the plan.
Here's the issue that so shocked the Dutch:
Dutch pedophiles are launching a political party to push for a cut in the legal age for sexual relations to 12 from 16 and the legalization of child pornography and sex with animals, sparking widespread outrage.
I freely admit that the slippery slope argument is a bit silly because just about anything that is appropriate can also be taken to illogical extremes. That is, the threat of a slippery slope is seldom a justification, on its on, to stop a proposed policy. However, some slopes are anticipatable (is that a word?) and I'm not surprised at the latest extreme in Holland.
UPDATE: Here's an article about the slippery slope from the point of view of polygamy and its damaging effects on a functioning democracy.