I don't know about annoying neighbors and smells. That seems to be a design and engineering issue.
If you live in a lower income area, get used to your condo/townhouse occasionally smelling like marijuana and/or tobacco whenever the neighbors decide to hotbox. Also get used to arguments and loud music late at night on weekends.
> That seems to be a design and engineering issue.
I'm sure you could build hermetically and acoustically sealed condos that keep out all unwanted noises and smells, but those sound like "rich people" condos that are not very economical.
If those issues go unresolved, that's a dereliction of city government and apartment administration duty.
Not to mention public transit is dirty and unsafe in any major city in the US because there is way too much tolerance for disorderly and disruptive people.
Having lived in a Berlin Altbau flat, in a dense central neighbourhood, I can say that's not the biggest problem. At least not when at home.
Crappy neighbours are. For both noise and smells.
Techno blasting behind the wall. Arguing families and shrieking children, through the wide open windows. Passionate cigarette and weed smokers (plenty of them in Berlin). Smoke from cooking wafting through the Hof.
This is even a bigger problem if you are unlucky to have to live in a commie block (pretty much anywhere in Central Europe). Even more neighbours, even denser.