This fallacy occurs when one makes the assumption that, because one concession is given, a "slippery slope" will be created that allows more extreme concessions to follow.  It is sometimes called the "Domino Effect" or the "Camel's Nose" Fallacy with the logic being that, if you are in a tent in the desert and your camel is outside, you should never allow your camel to even stick its nose inside your tent because, the next night, half of its body will be in your tent, and, the night after that, it'll be sleeping in your bed, and you'll be forced to sleep outside.  This is a fallacy because there is no reason to believe that, by letting its nose in the tent, it will eventually be sleeping in your bed forcing you outside.  All you have to do is draw the line and make it sleep outside the next day.  Any further concessions to the camel would be your own fault.

Example: "If we allow the government to infringe upon our right to privacy on the Internet, it will then feel free to infringe upon our privacy on the telephone.  After that, FBI agents will be reading our mail. Then they will be placing cameras in our houses. We must not let any governmental agency interfere with our Internet communications, or privacy will completely vanish in the United States."

Such thinking is fallacious; no logical proof has been provided yet that infringement in one area will necessarily lead to infringement in another.  This is no more logical than claiming that a woman buying a single can of Coca-Cola in a grocery store would inevitably go on to buy every item in the store, helpless to stop herself.

Example: If I let the dog have one scrap of meat from my dinner, we'll head down a slippery slope.  Eventually, I'll give the dog two scraps, three, four... soon, a place at the table will be set for the dog, and she will be hogging all of the white meat.

Couldn't I just be disciplined and make a point to never give the dog more than a scrap?

Example: If Mr. Spagnolo allows students to leave class one minute early today, tomorrow it'll be two minutes, Thursday it'll be three, and, eventually, we just won't have class.