Yes I agree, I hate the "their parents are together so..."
Firstly, that argument always assumes that their parents are living in marital bliss. I can assure you, I was not "lucky" when my parents were together. It was horrible, constantly arguing and screaming at each other, stealing the house phone to ring relatives to come and rescue me because they were fighting again and I was scared and so on... Anyone who thought I was lucky simply because they slept in the same house would have been kidding themselves. We've usually no idea whether the RDC are lucky or not.
Secondly, a lot of the time on here we can be talking about very young "new" DC, often toddler age even. Who really expects a toddler to consider themselves lucky because their parents are together.
And lastly, whilst I'm not saying no children will ever think this way, a lot don't in my experience. I remember all my friends thinking it was so cool that I got 2 of everything etc... It's stupid now as an adult, but that's how my friends, as children, thought. Likewise I often thought what their setup was was "cool" for a variety of other reasons, some having a sister when I didn't for example, the only child who didn't have to share anything and so on... all things now where I may look back as an adult and think there were pros and cons to all of our situations which I didn't understand or see as a child and neither did they.
It's not the same as saying all kids are stupid and don't understand anything which poster's get accused of here a lot. But I do think people place the emotional intelligence of adults onto children on these boards quite a lot and I don't think it really helps anyone.
It works both ways of course. But again this is why I struggle so much with this topic. A lot of poster's refuse to take an OP at face value about how she/he who actually knows their DSC in RL are reacting to things because they apparently know how they must be reacting to something because all kids are impacted the same... When actually they are often not imo. There's too many variables. It's a really hard topic to get advice on, theirs too many varying opinions on the right way and what that looks like often with no room for seeing anything from the other side.