That's not how evolution works. If evolution builds a mechanism to make you respond to a certain stimulus in a certain way, then it's more work (and more unlikely) to then make that mechanism only act under certain circumstances. We wouldn't not cry in private unless there were additional fitness advantage to it.
The appendix seems to be a counterexample to this philosophy of evolution. Useless body parts exist. What are the chances there are no useless behaviors? (By "useless" I mean "no fitness advantage.")
Not sure I agree wholly with the GP, but recent theories suggest that the appendix does in fact serve a useful purpose. It can act as a reservoir for gut bacteria that are necessary to our digestive health. It helps repopulate gut flora when they get wiped out by illness (often caused by other bacteria) that causes a bad case of the runs.
