One sentence: I do not like being vomited on in the night
Or weed on (under)
Or sleeping next to a smelly, milk sodden pillow that then ahs to be thrown away
or kicked by a horizontal child
Or falling off the side becuase my two lovely children are sprawled across the whole bed!
But on the other hand...
I have had much better sleep with them in the bed.
I have not often had to get up to deal with stuff at night.
I know where they are and if they are safe, happy, healthy.
Lastly and I feel most importantly, for us as a family - they have disadvantageous circumstances, being with a depressed single mother. I am often occupied in the day and unable to direct too much attention toward them as I am doing the stuff nobody else will - like decorating, gardening, housework, shopping...etc etc.
And I found that despite the emotional insecurity this scenario was potentially engendering, things for ds1 were Not That Bad simply because at the end of the day, Mummy was still very much a physical presence. I was there for him in the night even if I'd hardly played all day. It was the one time he 'got' me.
I really believe that this made the difference between a rather wild, scruffy, slightly cross little boy, and a child who was pretty disturbed and very unhappy.
Just in our case of course. I couldn't send him off to sleep alone as well as having to put up with my moods and so on during the day! But I think in a more secure set up with a non depressed parent, children might find they function fine sleeping alone.