Heh heh, I'm sure you don't mean to be insulting, but I sincerely doubt that this topic could involve anything I can't wrap my head around
I can see dirt acting as a barrier of sorts with regard to, say...some bird-bombs, but the "moisture retention" and "abrasives sitting on the paint" factors outweigh that for me. Maybe we just have different priorities.
See, I simply view "unwashed" as being a form of "poorly maintained". In my area, unwashed vehicles rust out due to the moisture/salt-retention issue. Period. Simple as that- UNLESS they're properly/thoroughly rustproofed, and that's awfully rare.
If you're assuming the vehicle *was* properly rustproofed, then that's different and maybe we don't disagree all that much after all.
I guess it's a pet peeve of mine in part because I had to replace all the fuel and brake lines (no longer available, had to all be custom-made) on the '93 Audi because the previous owner's so-called detailer didn't keep those areas clean. Even the tunnel wash's undercarriage spray would've probably done the trick.
OTOH, the old Volvo I inherited was run through the tunnel wash regularly, including the undercarriage spray. Yeah, it was marred up, but it was also rust-free, and still is despite decades of use in winter salt. And I compounded it one time after I got it, and it's still looking swell today for its current owner. Looks better-than-swell IMO for a 30-some year old car.
I do agree with you *in the short-term* though, it's just those long-term ramifications that I've learned about the hard way.
And OK, I guess that the marring from "rub against a dirty car" vs. "crappy wash technique" could be a toss-up, but I'd hope that any Autopian can wash (at least relatively) marring-free even if that means just running it through a touchless (with all the product-related risks that can involve).
And no, I'm not trying to be contentious, I just don't want somebody who believes everything on the internet to say they "read on Autopia that you don't have to wash your car..but now mine is all rusted out!".