Quoting wombie:" that is exactly right! It is said over and over again in alot of the research that pertains to the psychological ... [snip!] ... and how it really does play a role in providing that security and creating the trust that is so vital to infant development."
Edit: I need to clarify that I'm talking about older children here. I definitely co-slept with my son and it was amazing but now he's going on 18 months and wants nothing to do with me in bed which is a HUGE relief. At this point the only reason I want to co-sleep with him still is because of what I
want and not because of what's best for him. He's more than fine in his own room and actually seems to prefer it.
I co-slept with my parents for 10 years and all it got me was insecurity. I was terrified of being in the dark alone and incredibly needy. They did me a HUGE disservice by letting me stay in bed with them for years and years. There comes a point when co-sleeping becomes more about the parents wanting comfort than their children, at least that's my opinion. When you see a couple sleeping with their almost adult-sized children it just becomes weird no matter how you slice it.
With that being said, co-sleeping with a young child is wonderful as long as goals are set and expectations are had. I wish my parents had kicked me out of their bed by the time I was in elementary school. I can even remember how hard it was for me to sleep at friends' houses because I was so used to being with my parents and no one else. It was a huge handicap and that is spoken from firsthand experience as a person who stayed in their parent's bed for far too many years.
I realize everyone is different so there's no way you can say a child should stop sleeping with his or her parents at a certain age but I do know that it probably isn't a good idea to keep older children in bed. I totally understand co-sleeping with younger children though and I definitely miss sleeping with my son.