The fallacy part of the slippery slope fallacy isn't that it can't happen, it's just assuming that it applies to everything because it applied to one thing.

Everything about society is arbitrarily deciding who can and cannot do shit. You can't practice medicine without a license. You can't get that mortgage without a good credit score. You can't drink if you're not old enough.

It never progressed to the point where nobody could practice medicine or get a mortgage. At one point they actually tried to say nobody could drink but that didn't last long before everyone soundly told them to fuck off. So there's nothing inevitable about the slippery slope in every case, some things just naturally stop at a point the majority of society agrees is reasonable. It depends on the context and the process.

In the case of restrictions, that's a zero sum game, if you're saying there's a slippery slope of increasing restrictions then you're precluding the possibility of a slippery slope of removing restrictions (E.G. gay marriage -> transgender kids -> legal pedophilia) Unless you're advocating the very specific case that the the status quo is incredibly unstable and balanced on the knife edge of snowballing in the direction of whatever change comes along first.

A slippery slope of restrictions affecting an ever increasing number of people is not a natural situation, each step is harder than the last as an ever larger number of people are directly affected and will naturally resist it. It takes a considerable amount of social engineering and then some muscle to silence the dissenters who resist the conditioning to keep that process going beyond the point where it affects a majority of people.

But a slippery slope of removing restrictions on ever smaller groups can happen naturally in some circumstances. People obviously won't resist fewer restrictions on themselves and people don't naturally resist lifting restrictions on others unless they believe those others will do harm without restriction. If the biggest group of a collection of groups considered to be equivalent and potentially harmful manages to get the restrictions lifted and proves not to be harmful, then it can trigger a cascade where people no longer believe that the smaller groups will be harmful without restriction if the bigger group proved to be safe. Problems can happen there if society at large mistakenly lumps inequivalent groups together, such as believing gay is the same as transgender is the same as pedophile.