Go check out what happened when Buffalo NY built its rail. That is a perfect example and the entire downtown died.

I think you're scapegoating the rail and the real problem was that declining rust belt cities just suck.

See also: https://www.buffalorising.com/2007/10/what-really-killed-downtown-retail/

Glad you agree. They aren’t safe and rarely a good option. Forcing cars to make sharp turns and pedestrians to walk longer distances in the road to cross.

No, everything you wrote is wrong: roundabouts are relatively safe because they minimize path conflicts, forcing cars to make sharp turns (and thereby slow down) is a good thing, and although pedestrians walk longer distances around the edge of the roundabout, the crosswalks themselves are generally shorter and thus safer.

The reasons I think roundabouts are overrated have nothing to do with safety and everything to do with lack of space-efficiency and how the good performance for cars comes at the expense of other street users' convenience (e.g. making pedestrians walk farther).

Congestion taxes. They don’t impact somewhat wealth-off people like me since we can adjust our schedule. They punish poor people who can’t. It isn’t even regressive, it is reverse-progressive.

Oh, that's what you were talking about? Never mind then; I agree with you on that point.

Discouraging people from driving in downtowns needs to be accomplished by physically choking the traffic off with road diets and traffic calming etc. "Lexus lanes" not only create unjust privilege, they also fail at reducing capacity since they're just shifting the usage from one cohort of drivers to another.

Gentrification and white flight. I suspect you knew damn well what I was referring to but enjoy backwards arguments

No, I really didn't. What confused me was your use of the word "force." Nobody's forcing upper middle class people to do a damn thing. If they're moving to impoverished areas and gentrifying them, it's because they saw an opportunity they liked and took it. Conversely, if they're engaging in white flight, they're being "forced" by nothing but their own bigotry (which obviously doesn't count).

The upper middle class people have all the power in the situations you're talking about. Painting them as somehow the victims of their own choices is laughable.