Where I live, summer rain doesn't really clean the car (if that's what you care about), and in the winter you are shortening your cars life by years if you don't try and get the salt off regularly.
I bought the car. It easily lasted another 7 years before it died in a collision.
My car prior was a purely Midwest car, and I rarely washed it. It happily lasted 16 years. I passed it on to someone else, and he used it for a few more years.
I suspect the fear is overblown.
I'm 62, and grew up near Detroit. I remember cars developing major rust holes after just a few years. The rusting also affected the inside of the engine compartment, and it did make repairs more difficult. There was an industry of aftermarket rustproofing shops, that were a scam. Every teenager with a car (which was still rare) learned how to patch rust holes with Bondo.
My first car, the frame rusted out and had to be welded back together.
Toyota and Honda put a stop to that. They did a number of things: Better steel alloys, better coatings, painting the bodywork before it could start rusting, eliminating places in the body where water could accumulate, etc.
Today, you rarely see totally rusted out cars on the road.
But it really didn't make a difference to the longevity of the car. Sure, occasionally a repair was a tad more expensive, but that's it.
The frame, exhaust and suspension generally get corroded and start to fail. You see a lot of 200k Civics and Accords, but few 250k.
You really notice it when traveling to California. Last time I was in SFO with my son, he counted 78 Porsche 911s and about 100 “old” (80s or older) cars on the roads.
The salt from the road is driven by car tires into a briny mist that coats everything. It blocks vision through windows. It accumulates in chunks that can be kicked (like mud also can, except corrosive). It wicks its way into tiny crevices and betwixt layers and infects every part of the car that can be infected, and once there it rots everything that it can rot.
And I don't mean just the bodywork; that part has been getting better with improved processes and paint.
But stamped control arms often rust away while the ball joints and bushings are still in good form. Electrical connections rot. Frames and frame-like components often have scaly holes in them. Every exposed engine part corrodes; uncoated steel turns black, red, or brown; galvanized and aluminum parts turn white and kind of fuzzy (and stuck). Our junkyards are full of rusted-out hulks of cars with drivetrains that still work properly, even if they're ugly.
Fixing things when they break is tedious and time-consuming, and the most-sane approach to any repair on a car that's more than a few years old is to go into it with an expectation everything that doesn't crumble from rust is instead frozen with rust.
The work itself unilaterally causes a person a learn new facets of their verbal and mechanical vocabulary that they never even knew possible, and is arduous in ways that would test the emotional stamina of a Buddhist monk.
With enough cleaning and care (and just rinsing things off by driving in the rain), a car that is from the midwest can be largely saved. Getting rid of all of the salt slows the process down very dramatically.
But a car that is regularly driven in the midwestern winter is in the midst of a fairly quick process of being returned to the earth.
It's just a fact that is plain and that we live with every day. We do work to prevent it; on a warm-ish day in January, cars will line up around the block to get into a car wash and have a chance to dry out before ice freezes every orifice closed.
But it's not fear, I don't think. Just as we accept the sun coming up every day and disappearing over the opposite horizon every night, we accept the rot as something that will inevitably consume the most expensive machine that we own and that this will happen on a schedule that we play very little part in controlling.
From a certain perspective, maybe some people don't care if they would be getting rid of the car in like 5 years, but if you do want to keep a car 15 years and you live in "salt country" I would strongly suggest doing something about the salt regularly.
My first car spent its first 15 years in the Midwest. No garage. Very irregular car washes (perhaps once a year when I owned it). It lasted about 20 years total. When I lived there, I didn't know anyone who had to give up a car due to rust. There definitely was rust, but not something that caused the car to break down.
I used to think everyone does it, I will do at some point but that point never came. Inside we vacuum and wipe every few months. Washed mats once in an year or so but car body wash rain takes care of it.
Car wash is the only legal way to use soap, for better or worse.
And doing what with it, exactly?
The trapped oil gets disposed of separately, the treated oil-free water goes to the sewer.
AFAIK the regulations were put into place to prevent untreated water from going into storm drains and into the water system, so presumably the cities are fine if you pour it down into the bathtub drain and let it go to the waste water treatment plants.
But car washes are interesting systems and one of the things that makes them interesting is that the water they use is (often) recycled. The same water gets reclaimed and re-used to wash cars over and over again.
I didn't look very deep at all, but one car wash chain suggests[1] a reclamation rate of 70%. Not perfect, but way better than 0.
Given that by hand you use much more hot water than the dishwasher would, you're using more electricity (or gas). Since a little pump doesn't use much at all, it's mainly just the drying heat that matters. Though nobody is forced to use the drying cycle - if one enjoys drying dishes by hand, they can still use the dishwasher to do the washing.
Is it safe? Not for a restaurant where the temps need to get to parasite killing temps to pass muster.. but if I had to guess, the odds of getting killed by a bad-tempered cow outweigh it by 10x.
eg. Our household conserves water (we track every litre we bring up to the tanks and filter) and we don't have a dishwasher - hot water is heated by the sun and run-off goes to the grey water tank for the garden.
You save water and electricity.
You ever park under trees?
My (late) kid brother did that for a number of years. Big time sink and PITA.