What are your thoughts on sleep training?

we don't deprive baby of two mandatory needs- food and sleep. babies that rely on us for help to sleep will always wake up in the middle of the night (multiple times) and such disrupted sleep is terrible for their development. many parents often view sleep training as leaving baby in the lurch and they cry until they are so tired, they fall asleep on their own. this isn't true. baby cries a lot during the initial sleep training period because he is 1. very tired and want to sleep 2. doesn't know how to sleep and 3. hoping his cries will entice you to help him fall asleep (it's a viscous cycle). once baby learns how to self soothe (like us learning how to ride a bicycle) via sucking on their thumb/fingers, they will be able to put themselves to sleep and connect sleep cycles. since babies around the world are capable of learning the skill of sleeping from 3-4MO onwards, why should we deprive them of restorative sleep?