Someone accused by his interlocutor of using the slippery-slope argument should reply that the debate should not focus on the notion that cause A could lead to cause B—which is unremarkable—but rather, on how likely it is that cause A could lead to cause B. If recent experience is any indication, the slippery slope against which that interlocutor had protested is likely to unfold in all its decadence as the years progress.

Every now and then, a piece of philosophical theory breaks into the popular consciousness, such that people without any philosophical education regularly refer to it. One such theory is the rejection of the slippery-slope argument, which holds that an event, A, will set off a series of events culminating in some dreadful consequence, B—and therefore A should not occur. “The supposed ‘slippery slopes’ are fake, silly rhetoric to placate the faithful,” a columnist recently wrote, pointing to how partisans on different sides of contentious issues like gun rights or abortion take extreme positions. True, such arguments can sometimes ignore a potential middle ground and overlook the fact that the dreaded consequence will not necessarily follow. But slippery-slope arguments are not always incorrect, and they offer insight about the nature of modern progressivism.

Usually, rejection of slippery-slope arguments occurs in the context of their claims that some policy will have bad consequences. These claims may be wrong, but the slippery-slope label does not prove their wrongness. Societies slide down such slopes all the time: history is full of examples of nations that moved in a progressive direction over time, tended toward decadence or exhaustion after altering rules for elites, and then relaxed moral standards. Indeed, the slippery-slope argument, especially in the context of social decay, has a noble pedigree. Plato observes in The Republic that democracy leads to authoritarianism; as freedom and equality expand beyond orderly limits, only hardheaded authority can rein them in. The fall of the Roman republic to authoritarian empire and the rapid collapse of French republicanism before the rise of Napoleon stand as examples.

Today’s slippery slopes are more familiar. Consider contemporary discussion over the nature of rights. While political conservatives generally define rights negatively (freedom from something), progressives define them positively (freedom to something). The preservation of negative liberties is definite and circumscribed, seeking to conserve a particular thing; the search for positive liberties is less bounded, aiming to widen the scope of what is alleged to be true freedom. Contemporary progressives tend not to be satisfied with certain political victories, which, once achieved, give way to new demands: for example, activists hoping to secure rights for sexual minorities initially made assurances that those who disagreed would be left alone; now they intend to stamp out dissent and expand the universe of rights beyond gay marriage.

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