Why do conservatives keep on invoking the "slippery slope"?

As a conservative myself, I'd like an answer to this mystery -- even at the expense of posting one more item (I swear, my last) on the topic. The "slope" is by far, the weakest and least plausible argument against same-sex marriage (see my last post on the subject). Why won't it go away?

Here are five suggested explanations:

(a) Volokh's over-broad definition of "slippery slope": Gene Volokh defines "slippery slopes" to include any action A that will tend to lead to B (bad result). But that definition is language abuse. Example: The State's authorizing the immediate execution of all gay couples might very well lead to the legalization of same-sex marriage, as a sort sympathetic reaction. (Think about how the Holocaust led to creation of Israel). But it would be nuts to say that killing gays puts us on the slippery slope to gay marriage. Volokh, like many economically inclined conservatives, conflates causation and reason, probably because of an economist's obsession with revealed preference (action) and disdain for rationale. That handicaps his capacity to explain tropes that deal with rhetoric rather than result. (His ’03 piece on slippery slopes is otherwise a wonderful piece, by the way: It just is not about slippery slopes but rather about legislative dynamics).

(b) Confusion about the rationale for same-sex marriage: Obviously, if the rationale were that everyone ought to be permitted to marry anyone or anything that strikes their lustful fancy, then such a libertarian rationale would "slip" very far. But that rationale is a conservative straw man: The real rationale that dominates the discourse is precisely what I described in my last post on this topic.

(c) Confusion about the distinction between the Slippery Slope and the Tendentious Talking Point: Many conservatives simply confuse the tendentious talking point with the slippery slope. The claims on behalf of gay marriage might be mistaken: Maybe same-sex couples do not have monogamous relationships that partake of all the same emotional benefits as hetero relationships. (Roger Scruton made such an argument for difference in his book on the philosophy of sex). But this objection -- that the argument is wrong on the merits -- has nothing to do with the slippery slope.

(d) Bastardized Burke: Some conservatives think that all sexual traditions stand or fall together -- that once one begins to reason about sex, then the whole system of sexual regulation must necessarily unravel, because blind adherence to tradition is what keeps people on the sexually straight and narrow. Again, this argument might be right (I doubt it), but it is a mere claim about empirical psychology: It has nothing to do with the slippery slope, which is a mode of argument, not a worry about empirical prediction. (See comment on Volokh above)

(e) Activism begets activism: One might argue that, if one rejects possibility of procreation as a permissible basis for marriage, then one is necessarily committed to rejecting the ideals of romantic love as well, because both ideals are matters of perfectionist judgment that an activist could, in theory, reject. But being activist does not commit a judge to being anti-perfectionist: So long as one believes that the process of Senate confirmation will insure that lunatic sexual liberationists do not sit on the High Court, the states' laws against bestiality and polygamy and such are certainly safe. The rule of law, of course, might be endangered, as Justice Kennedy deals out judgments by personal fiat. But it is simply implausible that his fiat will ever go much beyond gay marriage, for purely political reasons: He -- like his successors -- will always reflect mainstream elite opinion, and (judging by Oprah's book selections and, more generally, the taste of talking heads for the fiction of Ian McEwan), elites still seem to think that sappy ideals of monogamous romance are fine.

Is there anyone out there who has a different version of the “slippery slope” that I have overlooked? If so, I’d love to hear about it.