Changes since congestion pricing started in New York

I was living in London when congestion pricing was introduced and went into the West End the day before and the first day of and the difference was night and day. The difference along Oxford Street, Regent's Street, Green Street, etc was astounding.

And in the 20+ years the evidence seems to back up how much of a net positive it has been.

NYC congestion pricing took way too long because the New York Democratic Party sucks and, as usual, legal efforts were made to block it, much as how well-intentioned laws like CEQA (designed to protect the environment) are actually just weaponized to block development of any kind.

What's so bizarre to me is how many people have strong opinions on NYC congestion pricing who have never been and will never go to NYC. Americans love the slippery slope argument. It's like "well, if they make driving cars slightly more expensive in Lower Manhattan then next the government is going to take away my gas-guzzling truck in Idaho".

What's also surprising is how many people who live in outer Queens and Brooklyn chose to drive into Manhattan and were complaining how this changed their behavior. Um, that was the point. I honestly didn't know how many people like that there were.

What really needs to happen but probably never will is to get rid of free street parking below about 96th street or 110th.

Also, either ban or simply charge more for combustion vehicles. Go and look at how quiet Chinese cities are where the vehicles are predominantly electric now.

Why does the slippery slope concept surprise you? It actually happens often - banning smoking indoors, for example - started in just one city, once they tweaked the model and overcame the legal challenges, it spread rather quickly. Legalized casinos, same thing. Uber, drinking age, pot legalization, more. Why would toll roads or congestion pricing be different? (Idaho's Sun Valley probably already implements something similar). And ICE vehicles are definitely in many politicians' crosshairs, if you don't already see that coming in the next decade, you aren't really looking.

These would be examples of normalization, not a slippery slope. The OP's example makes this clear (from "congestion pricing in NYC" to "they're going to take my car," not "congestion pricing in NYC" to "congestion pricing elsewhere").

(Regardless, I think the answer is simple: congestion pricing is only economically viable when an area is simultaneously congested and has alternative transportation methods that would prevent the local economy from collapsing. NYC is one of a very small handful of cities in the US where this is true, although that's largely a function of 80 years of car-centric design. Maybe it will change.)

"normalization, not a slippery slope"

Sounds like an arbitrary distinction, but in any event, it was the OP who used "slippery slope" to refer to going from "congestion pricing in NYC" to "they're going to take my car."