It's not about being 'comfortable with density', it's about having a society where neighbours respect each other, behave decently, and keep noise/mess under control, don't keep setting the fire alarm off, etc.
The noise problem isn't limited to loud music and parties, just the noise of kids playing loudly and running around in communal areas can become infuriating to neighbours.
Even if you've got good neighbours, there's other downsides with flats - a lack of parking/EV charging, often nowhere to safely store a bicycle even. No space to install personal 'green tech' such as solar or a heat pump. No garage/shed to store tools/bikes/hobby equipment.
How about compared to Europeans? Japanese have a totally different nearly pseudo-feudal culture that enforces submission and conformity ("the nail that sticks out gets hammered down"). Among western states which share a more individualist culture with the US, I don't think there's all that much difference in behavior.
The noise problem isn't limited to loud music and parties, just the noise of kids playing loudly and running around in communal areas can become infuriating to neighbours.
Even if you've got good neighbours, there's other downsides with flats - a lack of parking/EV charging, often nowhere to safely store a bicycle even. No space to install personal 'green tech' such as solar or a heat pump. No garage/shed to store tools/bikes/hobby equipment.