When I got pregnant and enrolled in our insurance company's well baby program, we received two free books: What to Expect and The Expectant Father.  The Expectant Father was a nice touch, a way to say to the expectant dads, you're involved in this too buddy!

As far as pregnancy goes, the father's role is obviously one of support.  "We" are not pregnant.

After the baby is here, with the exception of nursing, all aspects of childrearing including decision-making can be shared equally.  However, this is often not the case and the authors of The Expectant Father bemoan this current state of affairs.  Some of this is society's fault according to the authors:

Quite simply, Americans don't value fatherhood as much as motherhood.  Even the words conjure up different images: motherhood is equated with caring, nurturing and love, while fatherhood doesn't seem to be much more than a biological relationship.  As a result, men are rarely accepted if they assume a different role than the one they are "supposed to assume".

Then there are the barriers that the mothers put up:

Here's an all-too-common scenario:...their six-month-old-son started fussing.  Colin who was holding the baby began rocking him.  Suddenly his wife appeared and whisked him away.....What it seems to boil down to is that most of us--men as well as women--simply assume that women know more about kids than men....

Although most mothers feel that fathers should play an important role in the kids' lives, research has shown that they want that role to be not quite as important as the mom's.  In fact researchers have found that two out of three women seem threatened by equal participation and may themselves be subtly putting a damper on men's involvement with their children because they are so possessive of their role as primary nurturer.