Outside of a training-type dive, I believe that the DM shouldn'thave to be babysitting newer divers and making sure they don't hurt themselves.
By the same token, however, I think that a lot of the situations that people have been griping about on other threads regarding DMs could have been avoided with a proper dive brief, including some of the highlights of the dive. I think, especially for newer divers, we don't know what we don't know. Examples include some of these deep, narrow swim-throughs. If I don't know that the DM is planning on leading the group there, and surprise there it is, this can cause a situation. But if it is briefed that if those don't feel comfortable can swim over, or whatever, this can be benefitial to both those that want to do it and the others know how they can avoid a situation they don't feel comfortable with.
By the same token, we all have a responsibility to ourselves, and our loved ones, to know what we're getting ourselves into. If we don't feel we know enough about the dive site, or we're not comfortable with the conditions for whatever reason, we should SPEAK UP!