[mindcrime]

Yes, Hitler and Stalin spied a lot on their own populations for "national security" purposes, but we should be able to oppose surveillance on it's own merits with out resorting to the painting a (fallacious) slippery slope picture where the next frame is a KZ/Gulag camp.

Agreed, but consider this: a slippery slope fallacy is more like "If we do A, then B will inevitably follow". Lacking evidence to support it, that is a fallacy. But it's not a fallacy to point out "B" as warning of what might follow from "A".

And in the "reasoning by analogy" sense, it's not wrong to point out that "Group C did A and then B followed, so we might want to be careful about doing A" (assuming "B" is something undesirable).

Sometimes it is a valid point of discussion to point out these potential "slippery slopes"; it's just important to distinguish between the assertion that the following part happens as an inevitable consequence or not, and if that is asserted, to demand evidence.

[Karunamon]

The problem with such "pointing out" is that it's often taken as incontrovertible evidence that A means B will happen.

The very essence of Godwin's Law is that invoking Hitler is almost always the most extreme example possible of governmental abuse possible, when more nuanced ones would do the job. Usually it's a symptom of lazy thinking and lazy arguing, used by those who want nothing better than a cheap sound bite for their audience (e.g. "Obama is literally Hitler!" and other such gems).

By making the Hitler comparison, you are more likely than not pointing at an irrelevant extreme and tarring yourself with the brush of "conspiracy nutjob". There are better ways to make the same point which don't involve the same baggage.