A slippery slope argument goes like this: Action A leads to consequence k. Consequence k will, in turn, make consequence l happen, and l will make consequence m happen. While k is not an obviously bad consequence, l is somewhat bad, and m is potentially catastrophic. Thus, action A should not be done, because it will eventually lead to consequence m.
Sometimes slippery slope arguments are simply dismissed as fallacies, but it is obvious that they are not inherently fallacious. However, the strength of the argument is very dependent on the strength of the empirical evidence that the consequences one invokes will actually occur. Such evidence is often lacking, and that is why slippery slopes are often dismissed.
As a consequentialist I am very open to slippery slope arguments. If I, as a hedonist, make an argument about an action or a policy, and if someone can credibly claim that the action or policy in question will probably have bad consequences down the line, – even though the immediate consequences may appear good – then I would be perfectly willing to drop my argument.
Nevertheless, I am somewhat reluctant to take slippery slopes seriously if they are raised against me by people who are not consequentialists themselves; because even if I could counter the slippery slope with better evidence that removes the slipper slope, my antagonists would, presumably, not change their minds anyway, since their arguments do not depend on consequences at all. A parallel would be a scientific discussion where a pseudoscientist who rejects naturalism argues that the scientist’s naturalistic evidence is wrongly interpreted. However, if the pseudoscientist rejects naturalistic evidence altogether we would fell disinclined to take him ot her seriously in the first place.
I do understand, however, why non-consequentialists are eager to use slippery slope arguments, because it is mostly a win-win situation for them. If the argument is convincing, the consequentialist will have to drop her position. If the argument is unconvincing, the non-consequentialist can just fall back to her non-consequentialist principles and disregard the empirical evidence. For the consequentialist, it is, however, a lose-lose situation, since the non-consequentialist does not have to endorse the consequentialist’s position even it the slippery slope is successfully disproved.
In short, please bring up slippery slope arguments if you want, but do so in good faith. Be prepared to change your own views if the slippery slope does not pan out they way you thought in the first place. Otherwise, it is just like pseudoscientists (and similar folk) who argue against real scientists by invoking empirical evidence, while they themselves refuse to state clearly which empirical evidence might falsify their own position.