The only ones that can be blamed are the hijackers themselves.
It's pretty hard for a flight attendants to warn the pilots when your throat is already slit. And equally for the pilots.
None of the crew would have a chance on 9/11. Since then, regulations have changed and are about as good as they ever will. Just don't try to get around these regulations ... if you do, I'll be the first one to kick you in the tender place.