Interesting concept being out out here about the LSD. I'll try to only put forth my insights, as I don't see much value in arguing about driving styles and so forth.
I can see the ida odf an LSD helping, as the tip in on my 5 at least is pretty abrupt. Granted, it is the wife's car so I don't drive it much making the problem more common for more. I ca, however see that you might mash the throttle to try and get out into traffic. I have done this before and have spun the inside tire, requiring throttle modulation (darn wet pavement from the car wash!).
Now, my problem with an LSD on a Mazda5 is that it would help most in this type of situation: inside tire wheelspin, but this is a situation that can be "fixed" cheaper through ESP electronics. I imagine a big motivator to not offer this option is that ESP solve it for everyday driving and is part of the Mazda3 platform that the 5 is derived from. Yes, ESP isn't on the 5, but from a manufacturing standpoint, introducing another part (LSD) into an an assembly process that is basically the exact same as the 3 adds costs too great for Mazda.
The reason Mazda can make nice cars cheap comes from all that parts sharing. The entire lineup is similar enough that I can drive basically any Mazda without thinking twice about controls!
Also, (and this is more of a personal opinion), LSD units have never seems to catch in in cars. I'm really not sure if they just don't provide enough of a benefit, or what the deal is. It seems that the consensus is that and LSD acting on the turning wheels can result in unpredictable behavior for drivers not accustomed to it's operation and associated vehicle reaction.
I also have to admit that my experience with LSDs is primarily in RWD cars, mostly for going in a straight line for 1/4 mile. My dad's old '88 RX7 had one as well and I never saw much benefit from it in the few time I dove that car in lower traction situations as well. In the 5, I have usually been able to counteract wheelspin with either the 2nd gear start or a quick shift to 2nd gear, something the average driver will never use.