Inevitably some day a new way will be found to get weapons past security or circumvent flight deck security procedures.
When that happens, I'd rather the SLF jump the bad guys ASAP than make like docile sheep (and am I alone in thinking that some crew cultures, like the hijackers, prefer docile sheep to switched-on take charge types?).
Today the security types trumpet the effectiveness of their new and sometimes undisclosed precautions, but eventually the threat levels go down, the budget cutters go back to work and the security precautions become a victim of their own success... until the next outrage.
Budget cuts took out an effective air marshal force and will do so again:
See Armed and Anonymous in the current issue of Air and Space