I deeply apologise for the length; I wanted to provide (over)sufficient context while questioning my confusion and miscomprehension. Please advise if this can be improved or pruned.
Source: The Legal Analyst, Ward Farnsworth
p 176: A final example involves the use, against people suspected of terrorism, of coercive forms of interrogation—physical and mental pressure that falls short of “torture,” though obviously there is a lot of room for debate about where that line gets drawn. One argument against using any such pressures at all is an appeal to the slippery slope: if we get used to putting physical pressure on people, we will become numb to its horrors and dangers and will be inclined then to move on to more aggressive methods that would more obviously amount to torture; or we will start using torture elsewhere—against people suspected of other things, or against people convicted of crimes whom we want to punish regardless of whether they have any useful information. (The “we” here might refer to the police who do the pressuring or to the public at large.) All these things could happen, but it is hard to prove that they will happen.
176. How is the above an example of a slippery slope? Farnsworth submits that 'All these
things could happen', so why does it matter whether they will happen or not? Aren't these all truly cogent, coherent reasons, regardless of their probability of occurrence? What's "slippery"?
p 177: A path of this kind, with the right to die expanded in each case, was followed by courts in the Netherlands. The first decision by itself might not have seemed to imply the last one, but each step between them turned out to be slippery. This might have been so because norms of equality—of treating like cases alike—made it hard to draw lines between any two of them; in that case we might question whether it was a true slippery slope or just a case where the implications of the first decision weren’t fully appreciated until later. But it’s also possible that distinctions between these cases are available and plausible yet hard to draw in practice: each case presents heart-rending facts, and judges may not have the stomach or, perhaps, the moral confidence to say that any two of these situations are different enough to deny relief. If so, the result could amount to a true slippery slope: a case where decision two really was not thought to follow from decision one when decision one was made, but did follow from it after all.
177. If in actuality, decision 2 did follow from decision 1, then how's this a slippery slope?
As an addendum, I thought to link to https://philosophy.stackexchange.com/a/4683.