But we could start small, with just one neighborhood, a pilot project where the kinks get worked out and slowly scaled up. Getting permission for a small scale pilot shouldn't be impossible.
If you are worried about the slippery slope, then you are really worried that democracy does not work as intended. (And depending on where you live that may be a very reasonable worry). By the way, Nazi Germany was not really a surveillance state, perhaps you are thinking of East Germany?
Not really. That's a well established failure mode. People's perceptions can gradually shift as they become accustomed to the new way of doing things.
Personally I'd be less concerned about a slippery slope and more concerned about abrupt changes in policy. All infrastructure should be designed with the worst case scenario in mind. It's naive to assume that things will never get worse suddenly or that we will have plenty of warning or even a meaningful opportunity to react.
The thing about turnkey authoritarian solutions is that once something happens it's likely too late to take action. However there are often alternative solutions that physically constrain the system such that substantial abuse is impossible without time consuming and expensive physical modifications. The traditional speed cameras in the UK for example.
Cameras, AI integrated at the edge, software that can't be updated remotely, the full stack publicly audited, that only output video data when a suspected violent crime is flagged. Something like that might work. I'm not optimistic such a solution would see much support though.
You'd also probably want a policy put in place in advance to quickly pull them down if certain criteria are met. But again, I'm not optimistic about the prospects.