Slippery slopes legitimately exist wherever a policy not only affects the world directly, but affects people’s willingness or ability to oppose future policies. Slippery slopes can sometimes be avoided by establishing a “Schelling fence” – a Schelling point that the various interest groups involved – or yourself across different values and times – make a credible precommitment to defend.

http://lesswrong.com/lw/ase/schelling_fences_on_slippery_slopes