It's been 30 years since anyone sold a new carbureted production car in the US, for just as long cars have had OBDII, and it's been 50 years since cars were sold without catalytic converters.
There was a time, immediately after those technologies were developed, when older cars polluted significantly more than newer cars, but modern engine designs have been around long enough that cars old enough to be big polluters are expensive collectors pieces.
There may be an occasional car with a blown head gasket or piston ring polluting excessively, but they won't run for long in that condition. Thanks to CAFE standards increasingly limiting the availability of smaller vehicles in the US, the average 20-to-30-year-old gasoline engine probably pollutes less per mile than the average 0-to-5-year-old gasoline engine.
Downtown in US cities parking is prohibitive, but that is only a small part of the city. Most of the city you can park for free. You want to move the car every day just so it doesn't look abandoned, but otherwise this is a cheap way to live and you get transportation as a bonus.
At my current place (apartment in a suburb about 10km from the city center) our parking would cost ~180 USD per month. From a tech worker perspective it is not like unaffordable, but definetily a luxury for most of the population. The median after-tax income in Sweden is like 3k USD.
That tax I mentioned before also makes very old beat-up cars not worth keeping (which is the intent of the tax to be fair).
One of the main upsides of living in a detached house in Sweden is not having to pay for parking. But even so the increase heating bills in winter can easily cost more than a car installment depending on your HVAC and insulation.
Like god forbid some dude live out of a 2002 Town and Country that parks at a revolving series of strip malls eats a quart of oil every 2k.
The tent cities and the rows of campers are a different story (i.e. the density is the problem).
I think it should be permissible to allow some dude to live out of a 2002 Town and Country that parks at a revolving series of strip mall. I currently work with several people who use a similar method to keep themselves and their kids off the streets.
The phrasing might be bad in that I was pointing out the overall bleakness of the overall situation; no insurance, no registration, no maintenance, but the intent was to show that they are teetering on the brink of falling into an abyss that is very difficult to come out of, not that they were some sort of anonymous nebulous mass.
The main thing I have been struggling with personally with working with this issue (housing, addiction) over 25 years is that it is such a huge, seemingly unsolvable problem that no one is able to address systematically and when I think about the big picture I feel overwhelming helplessness, but find hope working in much more local situations.
The car comment was just an observation to the parent comment, with some additional commentary on how it isn't at all a big luxury, rather a bleak situation where the car owner is in a very precarious situation. Reading it now, I do see how it could be misconstrued as some sort of zealotry of people of a certain bent, but I think I am might be bent the opposite way of what you think!