Perhaps worth noting that a lot of the world is extraordinarily emotionally immature. Had I not spent a lot of time crying in CBT practitioners' offices, had i not joined Mumsnet and begun to read about what constitutes acceptable behaviour, I might have got to my current age (as opposed to just 3/4 of it) really truly believing that my parents know how to behave to one another and to everyone else in the world in a way that is completely useful, constructive and facilitatory.
Until I started noticing for myself that I needed to change my fairly stupid behaviour, noone else ever said anything. Or if they did, I didn't hear. None of us would qualify for Jeremy Kyle. It's just the naice suburban bourgeois shittery behind leadlight windows, people being nasty, selfish and immature, occasionally with awful consequences that just get brushed under the lovely woollen carpets; people being terribly unhappy but too intellectually superior and lacking in emotional and intellectual humility to actually go and sort things out.
So it doesn't surprise me in the slightest that people come on AIBU or Relationships describing the kind of shite that occupies me and my family every minute of the day. I see this kind of crap in a family that has no real financial constraints or really bad things happening to it. So under larger stresses of the more real, less privileged world, I can see DHs on AIBU being pretty horrible. Also DWs. etc.
Sadly, I think my mother/father/sister could each really do with counselling, CBT, joining Mumsnet, etc., but part of the problem with being unconstructive enough to get complained about on AIBU, is that you don't see the need to change your own behaviour.