Hitler seizing power and the Nazis invading Poland was also a fallacy. Until it wasn't. The NSA spying on everyone was also a fallacy. Until it wasn't. Go back in time and find other examples.
Any extreme powers you give the government to "keep you safe", they will eventually be abused, first against foreigners, political dissidents and whistleblowers, then against you.
History doesn't necessarily repat itself, but it definitely rhymes.
Technically, "slippery slope" isn't a fallacy. It's just a name for the idea that one thing leads inevitably to another. It's not fallacious to extrapolate from past experience, even if that extrapolation turns out to be wrong.
Arguing A->B is only a fallacy if no argument for the sequence is provided. A plausible argument was provided here based on prior experience of other governments. There's no fallacy if you just disagree on the probability.
Any extreme powers you give the government to "keep you safe", they will eventually be abused, first against foreigners, political dissidents and whistleblowers, then against you.
History doesn't necessarily repat itself, but it definitely rhymes.