[natalyarostova]

A slippery slope isn't a good or bad argument on its own. It's just the mapping of a physical model of reality to data. Whether it's a good argument or not depends on its fit! In some cases it's a very strong model. For example, free speech seems to work best historically when there are enshrined rules that are never infringed. Obviously the fit is not perfect (e.g. yelling 'fire' in a theater), but it's a pretty strong fit.

On the other hand, the model appears to fit pretty poorly for gay marriage, where they posit if you move from traditionalism, before you know it, people will be marrying dogs.