Denser housing sounds good in theory; I support it myself and vote accordingly. The problem is that it comes with other people. The more immediate neighbors you have, the greater the risk that one of them will be an antisocial asshole who makes life hell for everyone else. You're going to occasionally get drug dealers (or other habitual criminals), aggressive dog owners, serious mental illness cases, couples that have screaming arguments every night, motorcyclists who rev their engines at 5:00 AM, etc. And the police/code enforcement/apartment manager usually won't do anything to fix the problem. It only takes one bad neighbor experience to send a family fleeing to a single-family house in the exurbs regardless of costs or environmental impacts. So far I haven't seen the YIMBYs propose serious solutions to the antisocial behavior problem, or even acknowledge that it's an obstacle to their goals.