As a private enterprise, they have the right to restrict what they want. And they figure that more people that visit their site than not would not like looking at it. And if they are after traffic numbers for ad providers, they will do whatever gets them the most views. Capitalism at work.
And furthermore, I have noticed that a lot of breastfeeding moms just tend to be REALLY sitting on a cactus all the time when it comes to breastfeeding in public, general attitudes about breastfeeding in public, and that doesn't usually get news unless it is a slow news day. Case in point, this story
Although slashdot is made of very intelligent people, I know someone will say something about the first amendment in 5,4,3,2...