IMO it's better to find a way to soothe a distressed crying baby than to leave her/him cry. I offer my LO a dummy when he gets very upset - sometimes he wants it, sometimes he doesn't. He still goes on the breast ok as well....(although I do top up with bottles too). There are also theories that the sucking reflex is very important to be "lived through" as a child as it could reduce likelihood of additions (e.g. smoking) later in life. Of course, the sucking reflex can be satisfied by any means - fingers/thumbs, dummy, breast, bottle, piece of cloth etc - guess those theories really compare to the very old fashioned view of not sucking anything....