Snipped.
Attributing character flaws to the fact that someone is an only child is a form of prejudice similar to discrimination on the basis of sex or race. You are pretty much saying that a person was doomed to be flawed in a certain way due to a circumstances of birth over which he or she had no control.
A lot of research has been done on birth order, including surveys of whether or not there's any statistical support for popular notions about only children--that they are spoiled, selfish, doted on, put on pedestals, or highly disrespectful of others. None of these "character flaws" are found to be any more prevalent among only children than among any other group of children.
In birth order dynamics, an only child is 75% similar to an eldest child and 25% similar to a youngest child. A popular misperception about onlies is that they are mostly born to parents who actually wanted more children and feel so blessed to have had at least one that the child becomes the center of their world. Actually, onlies are also born to parents who never intended to have any children at all, but who declined to abort an unplanned pregnancy. Another segment of onlies are born to single mothers who never go on to marry or have other children, and these kids sometimes grow up feeling overly responsible for their single moms. Another group were born to mothers who underwent dangerous or very difficult pregnancies or deliveries, and these kids sometimes harbor a secret guilt over their belief (sometimes encouraged by the family) that they nearly killed their mothers simply by coming into existence. All told, it's not a significant majority of only children who are born to happy, grateful, well-to-do households.
I am an only child now 57 years old. I took care of my mother for 18 years, and my father for 9 years. When the parents of onlies age and lapse into frail health, there is only one child to care for them.
I grew up in a large extended family in which all the other branches had 2, 3, or 4 children. Only children were absolutely loathed in this family, and I grew up hearing all about my endless shopping list of character flaws caused by my own personal failure to have siblings. When I was a kid, if I fought with my cousins, I was spoiled and selfish and a bully who expected to get my way at all times. But if I didn't stand up for my rights and defend myself, I was weak-minded and weak-bodied because I never had to fight for anything and expected everything to be handed for me. If I valued my things, I had never learned to share due to being an only ... but if I tried to be generous, I was trying to buy affection because I lacked social skills due to be an only. It was just endless, until finally, when I was grown up to have a say, I quit having anything to do with these people entirely.
I ended up working for a sole propriator business for nearly twenty years. After fifteen years of employment, the owner finally confessed to me: I could probably sue her for this, but had I told her before being hired that I was an only, she would never have hired me. So she was glad I never told her, because I was the best employee she had ever hired and we became the best of friends.
For the record, I never sued her, spoiled rotten brat that I am.
As for TH being an only or an adoptee ... let's keep in mind that these are decisions that she wasn't at liberty to make about her own life. I believe she is guilty for whatever happened to Kyron ... but my belief is based on her own decisions and actions ... not on decisions that her bio-parents or adoptive parents made for her.