I do agree that in some cases it doesn't make a blind bit of difference.
For the very confident child who is happy to speak to everyone
For the child happy to leave his known carers (mum, dad, grandparents, whoever he's used to) for a period of time
For a child who doesn't need additional help with speech, or personal, social, emotional development, or socialisation, or physical development in areas where they don't have places to run around and play regularly.
It's not for everyone, and that's fine. The children I've worked with - all have massively benefited. But it's the parents' decision. If they feel their child is fine, that's great - many children don't go to nursery and are fine. For a great deal of children, though, it can do excellent things. Even if your child is social, happy, active, friendly, able to play with others, able to separate from the main carers - nursery can still provide valuable experience that will benefit them forever.
If you feel your child is too young, then don't send them. No one can or will judge. If you want to send them - I have seen 2-year-olds flourish at nursery. Develop their personality, their likes and dislikes, what makes them happy. And it helps with separation anxiety later in life. :)