For the most part, what you say is true Francis but there are always situations that change that. I had what we called a "doll crib" that I kept pulled right up beside my bed so that I could just reach over and pick my baby up to feed him in the night. It's not laziness. You have to stay awake (or at least try to) while you feed your baby who goes right back to sleep (if you're lucky) and meanwhile you are now awake and having difficulty going back to sleep. Sometimes I did keep the baby in the bed as I would drift off. My Mom taught me that you keep your baby on the outside of the bed on your outstretched arm as you cannot roll over on an outstretched arm. It works well. I am also a light sleeper so it's unlikely I would ever have rolled over on my child anyway. I can see where my husband could have and I would never have put a baby between us for that reason alone. I have woken in the night gasping for air only to realize that he rolled over on top of me!!! He has no memory of it but he's a deep sleeper. I can vacuum while he sleeps in ths same room.8OThis topic should be easy but...
It was a sore point in my marriage.. I was dead against our kids in bed and my ex wanted our newborn to sleep with us so she could more easily breast feed him.. To me that was just laziness..
There are many reasons I would not want a child in bed and only a few exceptions..
Personally I would love to have split beds anyway.. Two beds together so I can sleep a much better as I am such a light sleeper..
Second I was always against having our newborn in bed as I saw it as a dangerous issue.. Then I read an article that confirmed my belief that adults could (and I believe had ) rolled over and suffocate their newborn and that made it even worse..
As to when they get older, it is no doubt a no brainer as far as getting a better sleep.. Both you and your child are much better off in your own beds..