Well personally, I wouldn't. I bought a laser once with the intentions of mounting it on one of my handguns, but before doing so, I played around with it to see what faults I could expect.
Faults were many, in my opinion. On a black background, the red dot is very hard to see. I found that often I couldn't even determine if the dot was on the target or not. Bear in mind that you do not see the beam itself, only the dot where it is on an object.
Also, if you draw the laser up quickly, you have no idea where that dot is for maybe several seconds. You will find yourself swinging the laser (or gun, as the case may be) trying to figure out where the heck the darn dot is.
If it is dark enough where you can't see much at all, you will have NO idea at all what that red dot is on. All you will see is the red dot, if it is not on a black surface, but you will have no idea if it is on what you want to shoot or not. And if it is light enough that you can see your target, well, then why do you need the laser at all then?
On a carry gun, and under the circumstances of pulling your weapon in a self defense situation, I think that laser could get you killed. You will be much more concerned about figuring out where the heck that red dot is than you really should be at a time like that.