However I am not sure non-blood related nieces and nephews are quite the same.
This is such nonsense. Of course they are. One of my aunties, is married to my parents sibling. She has no blood nieces and nephews but I am very much her niece and a very close relationship with her and have done for over 30 years. I would be appalled if she thought less of me. My parents don't differentiate between nieces and nephew and I have nieces through my husbands side who I love very much.
Of course there are lonely only children, but equally there are people with siblings who experience loneliness. Siblings aren't some guarantee of a built in support system and in many cases as I see in my own job, are the cause of family stress and breakdown. I think there's some naivety among only children that if they had siblings, they wouldn't need to rely on anyone else which just isn't true. The nuclear family can't provide every we need. Siblings move away or have their own lives and it would be massively unfair to make one or two people responsible for being your entire support system. We all need friends and community.
This thread has shown that it's not the problem with only children or their parents but with people's outdated judgments about them. No one should have to defend or explain why they choose to have as much children they have. There's been similar threads on large families where people have commented they hated growing up in them and hated the lack of 1:1 time with parents and in many cases, they chose to have one child. It just shows no family size is perfect or better.
I always find it strange on threads like this, people arguing about a bunch of hypothetical situations. Absolutely nothing in life is guaranteed. Having an only child doesn't mean they are destined to a life of loneliness. Having more than one child doesn't mean they'll be a built in support for one another (it certainly isn't in my case). And as I've seen in my work in elderly social work, it really is 50/50 on whether siblings will support or not with this. I think the most important thing when planning your family is to have the amount of children you want and feel you can cope with whether it be one or five.
Of course as I've said some only children feel loneliness but so do people with siblings. And the research overwhelmingly points out to the fact only children turn out perfectly fine and are not less lonely than those with siblings.