you don't let them sleep by themselves for the first few months up to a year. the crib is just to create a safe zone for the child. you can't trip over and fall on their bed in the middle of the night, they can't roll out etc.  i believe a large percentage of sids deaths are the mother killing the kid however.  t. sleep next to my newborn son every night to make sure his all good and his mother gets a good night's sleep.
Australia