They were offered extra security by the military, but Chris Stevens refused. No one anticipated the attack, so no one could have rescued Stevens and the other three, but yes, it’s tragic that they died. Those guilty are the ones who planned and carried out the attack.
Chris Stevens asked that security not be increased:
readersupportednews.org/opinion2/277-75/21554-five-reasons-benghazi-wasnt-hilary-clintons-fault
Does that make it his fault? No, of course not. Again, the fault lies with those who carried out the attack.