Once can see how situations with pocketbook dogs can escalate - the aggressive creature has a go at someone's dog who then sees the need to defend himself or latches onto a pedestrian's ankle. No one wants that.
And when you express concern at the irresponsible owner it's you who is the bad guy. Not the neglectful owner, because in America intent counts. You could have restrained your anger, but look at the poor little dog, it doesn't know what it is doing. (No, it doesn't, it never learned and it never occurred to anyone around it that it should learn.)
Everyone immediately perceives that large dogs require constant attention and handling skills, but the less immediate but very real dangers from small dogs are downplayed.