Let's see, by comparison most handgun calibers and loads are anemic compared to most centerfire rifles or shotguns, so the better power choice isn't the handgun.
Lights can illuminate and provide a point of reference. Of course, handheld lights can as well. Sure, a handheld light can be held away from the body and in a large open dark environment, that certainly could be advantageous. Being able to handhold a light away from the body in the confines of a home interior with all of its corners and halls would be a really nifty skill - not impossible, but more difficult than with a weapon mounted light.
One of the really cool things about having lights on weapons is the ability to use them or not. They are simply another option. One nifty thing about them on home defense guns (long gun or handgun) is that if you need to do something with your weak hand, you don't have to find some place to stash the light, or how quickly, while your weak hand handles the necessary task.
Usually when right-handed shooters talk about using a handheld light, it is with the weak hand. The safety is that it can be held away from the body, usually being lateral from the body or high lateral.
Most bad guys are right handed as well. If they are inexperienced/unskilled shooters, they will likely have a flinch and that flinch will be low and left. So if the home owner is holding the light left or high left, the low left shooting by the bad guy very will may be right on target.
I don't like lights on firearms in a civilian environment.
Well, cops are civilians. If you mean by non-leo and non-military folks, I am not sure that their employment is such that their need to see the opposition in a combative situation is so much greater than our needs to see the opposition that a light would not be beneficial.
Personaly I think for HD a light just gives away your position, ...
Maybe. Then again, there are lots of folks who teach us to do things in such a circumstance that our positions would most definitely be compromised. Think about all those folks teach that teach Shoot, Move, Communicate. Think of all the instructors that teach that you need to give a verbal challenge to an intruder, the verbal challenge being such that the intruder may egress the situation or surrender before you have to shoot and potentially take another person's life that will change your life, forever. The verbal challenge also giving you one last chance to positively identify the perceived intruder as a real intruder. Certainly this was a lesson being taught for years at Thunder Ranch in Texas.
Think about all those who teach that the sound of a pump shotgun will often cause intruders to flee.
Such methods also compromise your position and the element of surprise. It just may be just the ticket to allow the intruder to duck out of sight and setup to ambush you.
Yeah, methinks a light would just be a huge neon arrow pointing to you and saying "Shoot here".
Of course, the light also says to the bad guy, "You are spotted and I can shoot you."
If you think about it long enough, there are pros and cons to just about every option in a self defense situation and what is a beneficial in one type of situation may be a detrimental in another.
