The “slippery slope” argument is frequently discredited- the term itself is discrediting. I’m sure someone must have used the term in a positive way but almost all references that come up on Google refer to the “slippery slope fallacy.” Eugene Volokh has an article taking it seriously, but I think that is the only readily available reference.
I’m not willing and perhaps not able to argue or analyze this in great detail. But I will give one example, a libertarian slippery slope using gay rights as an example.
The original argument for gay rights was libertarian. Surely, nobody could object to private behavior between consenting adults. What people agreed to do with each other in their own homes could not possibly be anybody else’s business. Other arguments were included in this. The fiscally conservative argument-Why should law enforcement resources be used in this way? The law and order argument- With serious crime rampant (this was the 60’s and 70’s) why should law enforcement resources be used in this way? The kindness argument– If a person’s heart should long for another of the same gender, why should they be denied happiness?
Essentially though it was a libertarian argument for negative freedom. If anybody had told you it would someday be illegal in Canada to quote the Bible on the subject of sodomy, or that opposing gay marriage would make you a censored person in polite society, you would have thought them crazy.
The slope was indeed slippery though. The next step was employment rights. It had been accepted for a few years that sodomy was not an immediate threat to the general welfare. But homosexuals were not protected against employment discrimination. If you thought them disgusting or evil you needed not give them a job in spite of that. But if the behavior wasn’t illegal, really, how could you use that as a reason not to employ a person? Even as a teacher of small children? I had some teachers who in retrospect were probably gay, and they were good teachers. That was not for me to decide though. Officially gays are not any greater risk of molesting children that heterosexuals. I remember seeing once on a cover of a gay newspaper an article that seemed to be about the noisomeness of age of consent laws, and the burden of sex offender registration. (This was a local paper in San Diego in 2005 or possibly 2006.)
The AIDS epidemic put an entirely new twist on things. Generally public health authorities track the contacts of people who have serious communicable diseases. If you have TB and don’t cooperate, you can eventually land in jail. AIDS was from the beginning a civil rights issue. The crucial thing was that AIDS infectees not be discriminated against, and thus their status must be kept completely secret at all costs.
More recently the subject of gay marriage has been an issue. Ten years ago this was a very hypothetical issue. Even strong gay rights advocates thought maybe it would occur sometime in the future, but were not sure if it was even necessary or desirable. Then the Massachusetts Supreme Court decided in was, in fact, an absolute and inalienable human right. In just the last few years this has become the liberal dogma. Being for civil unions is in no way a defense to the charge that if you oppose gay marriage, you are an evil person who hates gays and wants to kill them. You want to take rights away, and that these rights were invented by a few judges in a very liberal state is not relevant.
Liberals now say gay marriage will not be forced everywhere, and churches will not be forced to perform gay marriages, and to say they will is ridiculous. But history shows what today is supposed to be ridiculous will be a non-negotiable demand in a few years and firmly rooted law a few years after that.
The history of liberalism and socialism is the history of slippery slopes, most not libertarian, and I’ll try to look at those later. But if someone tells you A won’t lead to B, and saying so is paranoid and ridiculous, A will most definitely lead to B. There is a slope and it is slippery.