Bicycles and the law

I'm all in favor of sharing the road with bikes, but...what's with bikes trying to use pedestrian crosswalks? Either you're a bike or you're a pedestrian, not both. This happens frequently at Centre St. and Jackson Sq. Also, bikes seldom stop for pedestrians in crosswalks, or at red lights. And, I almost got run over yesterday on the sidewalk by a bike - when there was a bike lane on South St. only feet away. Come on!!!