I am an only, married to an only, with 3 of 4 (deceased) only parents. It is strange having such a small family when so much focus is on family time, especially around holidays. But other than that my experience is 100% positive and I am happy, and not lonely. Self-sufficient, enjoy time alone, have rich, rewarding friendships and regret nothing/blame no one. Please don't generalize your experience/perspective to suggest what's best for others. We all make choices and choose how to live our lives.
Please, if you're going to have one child, ensure that they have an active social life. Many friends are like siblings, and being well rounded is a good thing.
My sister and I don’t even talk and if we do it’s passive aggressive so I am basically an only and that’s why I have friends that support me