My first husband was not only an only child but doted on by his father’s four maiden aunts who shared an apartment several blocks away and were omnipresent.
He had cousins but was, as was his father, treated like the little prince at home.
During our marriage, he managed to make peanut butter and jelly sandwiches, served with milk and oreos, matzoh brie and once, instant coffer after he figured out that the boiling water went into the coffee and not vice versa. This with two Harvard degrees.
His mother wanted more kids and did have college-aged male borders in the house to try to mitigate the situation, but it was too little too late.
Getting back to the original question, I don’t think making a choice about the size of one’s family can be called either “selfish” or unselfish.” I had two and knew that a third would finish me, both physically and emotionally.