My apologies to those who want something more challenging, but here's a classic slippery slope from the Vatican:

VATICAN CITY — The Vatican is digging in after gay marriage initiatives scored big wins this week in the U.S. and Europe, vowing to never stop insisting that marriage can only be between a man and a woman.

In a front-page article in Saturday's Vatican newspaper L'Osservatore Romano, the Holy See sought to frame itself as the lone voice of courage in opposing initiatives to give same-sex couples legal recognition. In a separate Vatican Radio editorial, the pope's spokesman asked sarcastically why gay marriage proponents don't now push for legal recognition for polygamous couples as well.

I apologize for the lack of a direct quote and link, but the Osservatore Romano site does not have the article and when you search for the term "gay" nothing appears.  Curious.  Anyway, perhaps the Pope's spokesperson will remember that the slope leading to polygamy and polyandry hasn't already been traversed in the opposite direction.  Those things already exist, in other words, and it was straight marriage that led to them.

Gay marriage, being the opposite of straight marriage, will lead therefore ipso fatso apodictically to the opposite of the slope leading to polyandry and polygamy: monandry or monogamy.  That's the way logic works.