Why don't people take responsibility over their children anymore?

Today at the library today a physically disabled man was moving through the library and had his progress impeded by a child. The man also suffers from PTSD ( post traumatic stress disorder) and he shouted at the child. The library staff chastened the disabled man. All of this could have been avoided had the parents of that child taken responsibility over the child's actions and had taught the child manners instead of allowing the child to have free rein. Who do you think is in the right.