Sure. Personally, I don't like the idea for my kids. But professionally, I think it's a parental decision. This will not make a bad child or screw them in any grand fashion. This is a personal choice for each family. The question simply is - what do the parents want. If you don't mind, fine. If you do mind, then get to work on easing your children back into their beds.
Depends on culture. Within some aboriginal tribes of the rain forest it is common for the tribe to sleep communialy, in family groups.It is part of a culture that requires consensis for all decisions & holds individualism a taboo. Industrialized cultures prize self reliance & individual accomplishment.That starts with being able to sleep alone.If you want to raise a self reliant kid you help him learn to sleep alone.