Street space is a public good. It is literally land, surface area to be used for something. You can't create more of it short of demolishing all the existing buildings. Right now like 80% of the width of a Manhattan avenue is dedicated to moving and parking cars. Pedestrians and bicyclists are squeezed into tiny slithers on the sides. It's a total shame. If you count and compare the number of people passing a given point on a 5ft busy Manhattan sidewalk to the number of passengers in private cars in the 55ft roadway next to it, it's like a 10-fold difference in 1/10th the space.
Right now, everyone poor and rich at least has an equal access to drive on the roadway (assuming you can afford to maintain a car at all). However, midtown roads are already at full capacity all the time. There exist way more people in New York who would drive if they could, but they literally can't fit. It takes 1-2 hours to drive into Manhattan. This is considered "typical traffic conditions". Morning rush hour stretches into the afternoon and merges into evening rush hour.
Effectively, you are trading patience/time for the opportunity to drive in. For every one person who has the patience to wait 1 hour in gridlock, there are 2 more who do not and find alternative ways in. Even billionaire mayor Mike Bloomberg took the subway to work. It was described as "populist signaling" but it was literally faster for him than taking a limo.
Rich people have a lot of money and not a lot of patience. Lots of them would have loved to be able to pay to skip the gridlock, but they couldn't, until now. They have succeeded in taking this 80% of public space, that everyone with sufficient patience could access, and turning it into a private toll road. That's why this is a land grab! Doesn't matter if the fees go into a public fund - if revenue was needed it should have been raised by a progressive tax. A flat fee is the opposite of that!
The congestion charge will not even decrease the number of cars on the road. Remember how for every 1 driver there are 2 more who wish-they-were-drivers but who had more money than time? Every 1 poor driver taken off the road will be immediately replaced by 1 more private car service Suburban SUV. The rich crave travel away from us poors, in their padded armored tanks, and now they can do exactly that, as they have succeeded in having the legislature kick us off our public land.
The only thing that will reduce car traffic is shrinking the roadways. Take those 5-lane Manhattan avenues, take away one lane and convert it to protected micromobility lane. Take away another and widen the fucking sidewalks! Take away the street parking and convert it to green space with trees that survive longer than 1 year. Add loading zones for delivery drivers. Use the public street space for the benefit of the actual public!