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.
I disagree that with your last point, that people should make the argument purely on its own merits. "So what if people are monitoring our communications?" I might ask this question myself if I had never read any history books.
The worrying thing for me is that we've been here before. Hitler did not come to power via some dramatic coup. He tried that and it failed. Instead he took the long, slow, legal and democratic route. Many legitimate comparisons with early 1930's Germany are there. I'm not saying it's a facsimile, it never would be. But with each civil liberty we sacrifice in the name of security the state becomes more oppressive, more open to abuse, an evermore viable breeding ground for tyranny. Worst of all, it can all happen without a shot being fired and well meaning onlookers saying, 'It will never get that bad'.
I'm going on a bit now, but for me the really terrifying aspect is that with all our modern technology (which I do love) it is possible for the state to create an apparatus to suppress the population that which we could never extricate ourselves from.
To quote BoC, "Defend your constitutionally protected rights. No one else will do it for you."
No, that's exactly the problem. Other nations has at radically different time been in a vaguely similar situation.
Looking at Hitler doesn't tell you anything about the surveillance state that it doesn't also tell you about vegetarians and boy scouts. The reason we're not opposed to vegetarians and boy scouts (at least not based on their relation to nazism) is that we're approaching those cases on the merits. It's ludicrous to suggest a causal bond between those and Auschwitz.
Also, pure tactics: Anyone who's studied WWII civil oppression can spend hours detailing just how radical the differences between the Gestapo and the NSA are. You're basically handing your opponent the rhetorical petard he will hoist you by.
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.
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.
Back to the conversation, what might prove slightly useful from this comparison is that in the USSR and German Democratic Republic surveillance was mostly done through the use of one's acquaintances and often-times even close relatives, because as the article mentions back then secret police forces didn't have access to today's technology.
That's what made it very personal and invasive and what ruined lots of lives and close-relationships, while today's surveillance techniques seem to be (and I'd say they are indeed) more remote and not that soul-crunching. In the old system you risked to have your sister or brother-in-law snitching on you for listening to Radio Free Europe or for making a regime-related joke, you had to be always on the alert of what you were saying and to whom you were speaking. I think this is why in the present day and age we don't see lots of protests against this new surveillance system, it's far too remote from us so we tend not to notice it.
If not, instead of arguing by outrageous and irrelevant historical innuendo, you could express quite reasonable concerns about consequences of excessive security powers that are actually likely to happen.
It would be a much more convincing argument.
(since both the Nazis and the Bolsheviks very openly stated their intent to violently suppress people fitting certain criteria and had militant wings actually targeting them long before they achieved the power that enabled them to set the surveillance, I'm not sure the historical comparison even works...)
What about a president 10 or 15 years from now?
Yes, and too soon a lot of "healthy living" "outdoors" had too many single girls 15 or so coming back pregnant, as "Hitler's brides" and had to be throttled!