Some people argue that when a change in the law is being proposed, a slippery slope may result from the application of the new law. For example, in recent years one of the hottest publicly-contested debates in the UK has been about whether people suffering from painful terminal diseases should be allowed to end their life prematurely, or whether their friends and family can assist them in doing so if they are not physically capable of it. The Assisted Dying for the Terminally-Ill Bill was rejected in 2004. Its proposal was that a person, X, could be assisted by others to commit suicide if the following conditions were satisfied:
1. X is above the age of majority.
2. X is competent. (X needs to sign two declarations of competence, one in the presence of a solicitor.)
3. X has a terminal illness. {Two doctors must both assess that X has less than six months to live).
Now it might be that some people opposed the Bill, while simultaneously finding the applciation of the bill to be positive, ceteris paribus. However, they might also believe in a slippery slope conditional of the form "If this Bill is passed, it will lead to the passing of a more extreme and less desirable bill". Perhaps they only have a low credence in this conditional, but they evaluate the expected utility of the bill being passed and find that the stark probabilities for deeply undesirable outcomes out-weigh the benefits of the bill in the probably case where the slope isn't really as slippery as previously thought. Therefore, even though the bill, in a perfect world, should be implemented, because the world is not perfect its passing will have ill secondary causes or negative externalities.
A slippery slope argument of this sort might contain the following premise:
If the proponents pass their bill they will continue to want more extreme bills passed. Specifically, they don't really believe in this bill but they know it's more likely that they can get their more dangerous bill passed if they pass this first.
So the slippery slope argument seems to me to be more political than ethical. In the case of the assisted suicide bill, the opponents might argue that if it's passed it won't be long before any one of the conditions becomes unnecessary for assisted suicide, or perhaps unassisted suicide will be legalised. So these slippery slopers should take their argument up against the political system. "No more slippery slopes!" Perhaps they think that the general voting population is very naive and can be unconsciously corralled into adopting an extreme view, or perhaps they think it is the MPs who are this naive.
Sometimes we need slippery slopes to get quickly to the correct positions which are so far from the current law. For example, somebody may have argued that men should be allowed to wilfully engage in sex with each other, but only if they're over 25 and have the consent of their neighbours. A hundred years ago this would have been a progressive opinion and would probably have contributed to the situation we have today, which has only very recently given reasonably equal constraints on homosexual sex as to heterosexual sex. Had the person described above been able to view the future and seen what the first bill on extended rights for homosexuals would lead to, they might argue against the passing of that bill. We might still have those laws if everybody took the slippery slope argument too strongly.
