I'm not sure it's wise to compare apples to oranges, i.e., the needs and expectations of a 3 year-old are by no means comparable to what much older children much less adults need. This whole "start as you mean to go on" thing is often taken WAAAAY too far, otherwise, why not put 1 year-olds in "preschool" 5 days a week? Why not make 8 year-olds travel to foreign countries with little or no notice since that's what many adults who travel for business or in the armed forces must do. And speaking of what older chidren do, would you advocate homework for 3 year-olds, etc.
Babies and toddlers are not just small adults.
It does drive me crazy though when I tell people I'm considering elementary montessori for my daughter because I feel the learning style is suited to her and I want her to continue to love learning and not be turned off by the public school mentality they invariably say 'well she'll have to get used to it later anyway' as if not having them do it now means they won't be able to later.