Religion & Law

Reading the comments to my post on Will Saletan's distinction between SSM and incest made me wonder: are slippery slope arguments more powerful in legal reasoning than in moral reasoning?  Saletan was focused on moral arguments against (adult) incest, and there does not (in my view) seem to be much of an obstacle in making arguments distinguishing adult incest from SSM.  That doesn't mean you will find arguments in favor of SSM persuasive; it just means that there are readily apparent moral analyses of SSM and adult incest that are distinct from each other.  As long as those arguments are available, I don't see much ground for raising slippery slope concerns.  In law, though, there seems to be less and less moral analysis -- or perhaps more accurately, moral analysis has been foreclosed for certain categories of conduct under the Supreme Court's interpretation of the Constitution (Eisenstadt, Roe, Lawrence, et al.).  If law is pulling back from adjudicating contested moral claims regarding sex, the beginning of life, the meaning of marriage, etc. to the extent that these claims are perceived to implicate threaten overarching equality and privacy norms, then it seems that the slippery slope concern is apt.  Even then, though, it might not be a slippery slope per se, but an already flattened slope that is just gradually being articulated as particular disputes are adjudicated in the void that has been created by the law's departure. 

This is a long and rambling way of getting to the question: do slippery slope arguments have much traction in philosophy (or other circles outside constitutional interpretation)?  I'm guessing that this question has been taken up by others in the past, and if so, I'd appreciate being steered toward the appropriate sources.