The societal norms are powerful. We have an only child because of secondary infertility. I miscarried her only sibling. At the time, I was devastated and I felt dreadfully guilty that dd would grow up "on her own", despite not being particularly close to my own sibling.
However, as dd grew up, I realised that the only child stereotypes were a load of old bollocks. That dd was abundantly happy and thriving as an only child, with more self confidence, better social skills qnd a bigger army of friends than I could ever have dreamt of for myself.
I realised over time too that I had no longing for a second child. That being a parent to dd was 100% fulfilling my maternal instincts, that I loved the balance in my life and the ability to carry on with my career without feeling guilty, and that I actually felt that our family was wholly complete as it was.
And in more recent years, I have overcome the final hurdle that used to cause me sleepless nights... the fear that dd will be left to care for me and DH without support. Because now I am in that phase of life where I am caring for my own elderly parents, I am doing it alone despite having a sibling - as my mother did before me - and the invaluable support that helps me get through the tough times comes not from my family but from my very dear friends who are always there for me.
So yes, I only had one because I couldn't have another, but if I had my time again with total control over the outcome, I would absolutely be one and done, no question. I'm not sure that I ever even wanted a second child in the first place...it just seemed to be the done thing!