The slippery slope argument is NOT that people will find doing X to be a good thing and then will therefore carry it on to something bigger, but rather that just by doing X, we'll magically somehow slide all the way to hell.

The latter is what Tom is arguing in this thread. I'll give him some credit for being partially right when it comes to government programs, like military and prison building (and the ones he mentioned). A government program creates a constituency that fights to preserve and expand it. In that type of case, we have a mechanism for suggesting the program might get worse. Still, saying "maybe something bad will happen in the future" is a weak argument to add in the decisionmaking.

I mostly despise the slippery slope when it comes to morality/individual rights issues. Decisions on smoking, abortion, and gun control have limited effects on creating powerful constituencies like prison guard unions, etc.