>> Quad plexes by right [0 for example] makes a lot of sense to me. If you’re OK with a quad plex next door, IMO you’re not part of the problem
I would actually not be OK with quads next door to my house right now, because that is not the type of life I bought into. That may sound crazy so let me explain.
For 39 years, I valued density/walkability/convenience of city life, and lived in NYC for most of that time. Now that I have a family, I value certain other things in my life. We specifically chose a town that was "dense enough" but not "too dense" - zoning here allows neither mansions nor quads you're talking about. This has impact on things like - how busy the traffic is on local streets, how much green space there is, etc. Everyone who lives in this town chose it for the same reason.
Is not wanting quads next door NIMBYism? I don't think so... When I lived in the city, I wanted more tall buildings next to me, when I live in this town, I want more "this-town-style" homes next to me. Why am I ok with this? Simply because nobody moves to this town unless you want this life. If you want a more dense town with duplexes, triplexes etc, then there are other towns around us that are already zoned this way and people who live there want that. If you want even more density, NYC outer boroughs are just a few miles away. So people have choice.