>>"Yes, but what if you run into an actual slippery slope?"
This particular case does seem one where it would be entirely valid to have a discussion about whether it is going too far, but how much further one or other person might want to take things in future isn't really part of that discussion, since not only is it speculative, but it's clear that numerous changes to many systems which most people would see as justifiable could be portrayed in a way which, taken to an extreme would result in something people would find unacceptable.
That's the problem with slippery slope arguments - they're effectively non-arguments or discussion killers.
And as for slippery slopes in general, it does seem that people often assume that there's some kind of inevitable momentum involved even when there's no obvious source of such momentum, and that even though [presumably?] there's a point beyond which the situation becomes less and less desirable to more and more people, those people will lack the means to halt things or change direction. That doesn't seem to show a great deal of faith in people in general.
>>"I don't think that poor merit of other arguments should be a reason not to stand up against what's happening here."
I think the reasons for standing up (or not) against what's happening here should be based on the rights and wrongs of what's happening here.
>>"If you call this FUD, will you be honest and advocate dropping the PSI thing entirely?"
Relying on slippery slope arguments *is* relying on FUD, since it's bringing up frightening (or at least deeply undesirable) extremes and alleging that them happening is a *possible* consequence of deciding something now - "If you allow X, it's possible that scary Y might eventually happen".
It's a way of failing to look at the actual merits or drawbacks of X, and a way that a cynic might suspect is being proposed by someone who doesn't think they actually have a strong enough case against X without appealing to the slippery slope.