I am very aware of all of these. And yes, they are very real - the issue I'm trying to draw your attention to is that it's not logically reasonable to assume that legal precedent is a reason to hold back or push forward a decision, because while our decisions can be a slippery slope, and do set a precedent, it's not guaranteed. It's just a weaker structure for an argument when debating these topics, I think. The Wikipedia article on Slippery Slope fallacy can probably make the case more clearly than I can, but I think it really just has people spinning their wheels. Both left and right parties feel there's a slippery slope on nearly every hot topic.
There are cases where this kind of argument is sound, but only in the context of "if you do this, there will be consequences you may have not considered, and here's what could happen..." But in the context of political discussion, it suggests that the next outcome from the government is inevitable, when we know we can look at each issue, vote, talking point, etc. independently.