Excessive use of force: In IN, the def of lethal force is any level of force that can kill or permanently change the quality of life of an individual. Since lasers can permanently damage your eye if it gets shine in there, lasers could constitute lethal force when an actual shooting isn't required. (Lawyer babble was my instructors response to this reason).
Threat escalation: A suspect might see the dot on their chest and "freak out" and attack rather than give up if a gun were simply pointed at them without a laser. (didn't think as highly of this one either).
Target acquisition time: Many LEO's only shoot their guns once a year to qualify, without proper training, their firearms don't feel like natural extensions of their bodies, as a result, they look for the dot instead of just aiming and letting the dot be where it needs to be. When tested, most officers shooting times went up quite a bit with lasers since they were looking for the dots instead of using their sights or simply indexing their bodies. (although this does raise the point of: "if you're not looking for the dot, and are simply pointing your gun.... what's the dot actually doing?"
The biggest reason for not having them on LEO guns: "Who's dot is that?" If every LEO has a laser, and multiple LEO's are at a scene, how can you tell which dot is which? With adrenaline pumping, it's entirely possible to point your gun at a BG, see a dot, and fire, missing your target since it was another LEO's laser sight targeted on the BG.
Point #1 - Excessive use of Force. Commercial handgun lasers are less than 5 mW which means they are 'eye safe' for brief periods of time. If you have an officer that is intentionally trying to blind the perp then that officer has issues - he should be aiming center mass anyway.
Point #2 - Threat Escalation. Actually, lasers are Threat DE-escalators - the BG's see the red dot and know exactly what it is and generally back down - it's one of the rare things that Hollywood has gotten right. I don't care what color the BG is or what language he speaks - a red dot on your chest is the visual equivalent of someone racking a pump shotgun...EVERYBODY knows what it means.
Point #3 - Target Acquisition time. Lasers are much faster than tradiitonal sights for acquiring targets...ESPECIALLY if you're shooting from non-traditional stances (on the ground, moving, running, barriers). Lasers do require a little range time so you don't 'chase the dot' - but once you've figured that part out you can dramatically increase acquisition time and accuracy. This is one of my favorite points - if you're in a gunfight, are you going to stand there in a perfect Weaver stance, align front and rear sight on the target, practice breath control and gently squeeze the trigger? Doubt it - odds are you're going to be hauling a$$ looking for cover (away and diagonally from the threat) and returning fire as best you can, most likely one handed. Try getting a traditional sight picture when you're doing that.
Point #4 - Who's dot is that? Ridiculous. Unless you've got 20 guys surrounding a bad guy you can tell what dot is yours. Again, if you have time to marvel at 20 dots on a bad guy you've passed the point where a laser is advantageous (other than for Point #2 - Threat DE-escalation). At that point, you should have transitioned to your iron sights.
As far as lighting conditions, all lasers will wash out in bright sunlight - however, most armed encounters occur during low light or darkness so in most SD cases the washout won't matter. A red laser is actually better in dark or low-light conditions as you can't see the beam and trace it back to the source (unless of course there are any airborne particulates...smoke, fog, etc.) A green laser at night is literally like a light sabre - and you can quickly follow it directly back to the source. The best application of a green laser is during daylight, since green is the most visible wavelength to the human eye, it is easier to see during the day. Green is great for daylight plinking, not so great for SD.
There are three main categories of folks that use lasers:
1) Women - because in general they do not practice as much as men and quickly learn that they will hit where the dot is. I've tried to explain sight picture to my wife until I'm blue in the face and she just doesn't get it...however, she knows that when she puts the red dot on the target that's where she'll hit...and that's good enough for her.
2) Older shooters - folks with bi-focals who can't see all three sight planes benefit by putting the dot on the target - that way they're only focusing on one sight plane (the target).
3) Anyone who is serious about self defense. This is the group I'm in and I think of the laser as another 'tool' in my toolbox. It's there if I need it and I practice with the laser and without it. Anything within 21 feet gets the laser - anything beyond that distance and I should have time to bring the weapon up and get a 'traditional' sight picture with iron sights.
In regards to the companies, I would recommend Crimson Trace. Their lasers are built into the grips and if anything happens with the laser, the weapon will still function. On the Lasermax systems, you're replacing a critical factory component and I have had two of their systems break while shooting, causing a weapons malfunction (one actually locked the slide solid and took about an hour to get it apart...not good in a gunfight).
The other nice thing about the CTC grips is their 'instinctive activation' - the laser comes on as soon as you grip the weapon. In a truly high stress situation you will lose fine motor skills and simply will not remember to 'turn on' the other systems...with CTC the laser is on when you need it.
As always, YMMV, but this is what I've encountered through many training situations and practical use.
If you're 23 years old with 20/20 vision and put 1000 rounds a week downrange a laser may or may not be 'necessary' for you...but the vast majority of shooters will fall into one of the three categories above and will generally benefit from having a laser on their weapon.
they tend to get calm rather quickly. And by the way im an LEO as well
