In most TNG, VOY and even DS9 episodes, Starfleet security personnel appear to be slow, unprepared and tactically unimaginative when facing threats, especially intruders and boarding parties. Examples:
- Rather than convening at the nearest transporter room (because they insist that site-to-site is risky) and transporting strategically to corner the intruder, they walk hurriedly along corridors.
- They rarely take defensive postures or have quick reflexes and are often shot while standing.
- During physical struggles, they show almost no martial arts training (only exception is the chief of security)
- They brainlessly follow standard procedure and rarely use decoys or other indirect or deceptive strategies. They fall for deceptions all the time.
- They don't bother with amour (we have seen people taking cover behind things such as overturned tables, so there are materials that can at least limit phaser damage without weighing a person down too much).
- They don't use phasers in wide dispersal mode in situations that it would be useful.
- Tactical away teams are rarely camouflaged (exception: TNG: Chain of Command)
- Security teams operate without a dedicated controller guiding them remotely (instead, they haphazardly make radio contact with the bridge chief of security)
- And many other examples...
Out of universe, we have seen that later personnel, such as the MACOs and the alternate universe security personnel seem to do better. But seriously, after wars with the Klingons, the Borg, the Dominion and various other antagonists, how can Starfleet security be this poor? Surely there must be a clear line between being peaceful and being naive.