Sharing the sidewalk

Why is it we have this herd mentality that if we are walking in the same direction as a large group of folks we feel the need to take over the entire sidewalk, as if no one would think of going in the opposite direction? In my walk to my job I am usually going against the majority of the flow of pedestrian traffic and everyday it is like swimming against the tide. People coming at me, 3-4 abreast taking over the sidewalk making me serve to avoid them. I am just in my little lane on the right side of the sidewalk, which I thought was how you were supposed to do it, I am in danged or being overrun by the human tide of commuters. Moist expect me to mover over even more so they can get through. And God forbid if I don't turn my shoulders to let them through, never mind that they are taking up 3/4 of the sidewalk. All I want is my little lane! I feel ike Billy Crystal in the stampeded scene from City Slickers, where he is holding on to the tree for dear life. The one benefit to this situation is that I have increased my skills in moving through a crowd which comes in handy whenever I go to a Cubs game.