Why don't phasers have a safety that scans the user? We see multiple times people's weapons being used against themselves, and Picard was nearly vaporized by his. So, why can't the phaser DNA scan (not full, just enough markers) to tell if the person holding it is Starfleet, and then disengage the safeties?
I think this is probably going to end up being opinion-based, since it's really a technological question about technology that doesn't exist, but I can offer a little perspective as a computer security AND a gun guy.
Stuff like this comes up with proposed gun regulation and with military tech, and it's referred to broadly as IFF - Identification, Friend or Foe. As the Wikipedia article points out:
The term is a misnomer, as IFF can only positively identify friendly targets, not hostile ones.
And there's the key - IFF can only identify friendlies, not identify hostiles. So now, consider the following scenarios:
- Friendly turns philosophically hostile.
- Friendly is bribed hostile.
- Friendly is coerced hostile.
- Friendly loses control and becomes dangerous (think munitions more than people).
Those are fairly down to earth possibilities. Consider these:
- DNA is spoofed to match friendly (this happens in the real world with IFF)
- Friendlies are affected somehow so that their friendly IFF signature doesn't register.
Some last points from other dangerous hobbies on why "safer is less careful":
- There's a table saw on the market right now that will stop (and destroy, incidentally) the blade if it comes in contact with flesh (it's measuring the eletrica potential of flesh - they use a hot dog to demo it). Do you think people will be more or less careful around that sawblade than a regular one?
- Blacksmiths don't wear gloves to protect their hands. The reason for this is that if you touch something super hot with a bare hand, you'll drop it, and have a little burn. If you touch it with a pair of gloves, by the time the heat registers through the glove, your glove is on fire, and will burn that hand AND the hand trying to pull the glove off with.
Weapons and dangerous tools are designed to accomplish a certain task, and at certain point, you just have to accept that they aren't 100% safe - if you push towards that 100% safety level, you AT LEAST compromise their effectiveness, and at worst you make them even more dangerous, or more likely to be operated in an unsafe fashion.