Solving the automated driving problem will require these systems to behave in ways that regular human drivers consider acceptable - at least for a transition period of time where both live on the road together. Sudden hard breaking in situations that humans see absolutely no need for it is an unacceptable behavior for human drivers to have. Just because it's not your fault doesn't mean you can't do things to prevent it. I have prevented many crashes throughout my life due to my mitigations around others' driving mistakes. We should expect self driving cars to do this at least as well as - not worse than - humans.