I love children as much as the next person (no, I don't, I love my own children, other children I tolerate - if they are well-behaved and chew with their mouths closed....), and I think parents deserve to live in the same world as the rest of the people, with the same rights in public spaces, but if your child is screaming his head off and has done for the last 30 minutes, in the cafe where everyone else are trying to work - chances are you should probably consider taking him out for a walk instead.
I feel sorry for the little guy though. His mother doesn't seem to understand that the answer to his cries are not to rock the stroller ferociously side to side while mouthing "hush" in a very loud voice and throw books and stuffed animals at him.