A manager's nightmare

I was having a conversation with some friends who told me quite plainly why it is that women are so often passed up in the career world.  The reasoning is based on a lot of assumptions, so naturally it makes perfect sense and is applicable in all situations (where's the sarcasm font?).  

Number one is that when you are looking to hire a professional a manager's worst nightmare is that they put X amount of TME (time, money, and energy) into an employee who they EXPECT to keep on a short leash for the next 20-30-40 years (corporate slavery).  The manager looks at a man and says, "great, unless you get killed or horrifically mangled, you're coming in to work every day for the next 30+".  The manager looks at a woman and says, "hmm, sorry ms. X, seems to me that you could get pregnant and then I'm going to have to still pay you while you give me nothing.  How am I supposed to maintain my inflated salary with you draining my TME with your family?"

This is not fair.  Not all women even have the desire to have children, but it seems like managers across the country are trained to believe that a woman won't follow through with a career.  It's a disgrace, how do you remove such a huge gender bias?