Leftists in general tend to be this way. I've watched tragedy of the commons destroy several well-intentioned community projects. They can never seem to get around that there are people who are assholes and that these people are either utterly feral or are completely venal. These people need enforced rules in order to participate in society or keep them out of it completely. But leftists tend to believe in tabula rasa, that experiences write who a person is, therefore if they were in a good environment they will just behave nicely. It's very naive. So they step over the homeless and crack pipes in the entryway of their bughive and tell themselves polite fictions about it.
That's not even a proper application of tabula rasa, being "raised" in a good environment is very different than "being" in a good environment, it's literally the difference between raising an animal in captivity and dropping them in a room full of toys and food, they will behave very differently.
The biggest problem with blue cities and left-leaning communities is as you mentioned—the line on what is and isn't acceptable behavior is never drawn (and I'm talking modern Western left ideals, China and the USSR have/had some decidedly left-wing ideas and politics but anyone that crossed that line was swiftly dealt with).
And yet, most of them spend all day isolated inside their pods posting on reddit and watching YouTube videos. Maybe they think if people are forced to interact with them they'll magically make friends?
When I think of my college experiences, not one of them has involved making friends on the campus bus line. Classrooms, sure, oftentimes I ate lunch with basically complete strangers, but if you extrapolated those...eating at restaurants or making friends at work, those are in the suburbs too. And when I talk about restaurants, I am referring to actually eating at restaurants...not getting delivery, carry out, or drive-through.
And with the "true" urban restaurants being cramped and ready to rush you out the door, why would they? (See my previous
post on the issue). Most of the food experiences urbanists tend to talk about are bodega kitchen options (mogged by any half-decent modern gas station convenience store, cheaper too) or overpriced food trucks.