The reinforced locking doors were certainly a reaction to 9/11 but I disgree that they were not carefully considered. No solution is perfect. The reinforced doors and locking mechanisms prevented some possible risks and introduced others. These new risks were doubtless considered and thought to be far less likely than the ones that were prevented, and thus a resonable trade off for the benefit provided, as nearly every safety and design decision is.
Life is not risk-free and it cannot be. We can never assure 100% safety.