I feel that all three popular shotgun gauges have their place in the role of defensive tools.
I happen to favor the .410 when properly set up for the task.
Here are the pro's as I see them.
#1: Light weight firearm.
#2: Low recoil even with serious defensive rounds.
#3: Ease of use by a wider section of shooters in regards to age and physical capabilities.
#4: Lighter weight ammo that has more than enough punch for it's size.
As with everything else in life there are down sides.
#1: Pellet count is low with defensive ammo due to case size.
#2: A cylinder choke barrel is needed for the best patterns when using larger projectiles.
#3: Pump and other repeating actions are few and far between, most are DIY projects.
#4: Few acceptable defensive loads on the market.
The .410 can work as a defensive arm if the shooter does his/her part. The majority of defensive actions happen at extremely close ranges inside a home or apartment, which does negate some of the down sides to using a .410. The inherent low recoil of the cartridge seems to be a good answer to the problem of finding an arm suitable for all members of a family.
Bottom line for me is versatility, you can do a lot more with a 12 or 20 gauge.
The way I view the three gauges are like this the 12 = .338, 20= .30-30, and the .410=.5.56/.223 rem
To me it's all about picking the right tool for the task, the right tool for the shooter and going from there.
A 12 gauge will not penetrate like a 5.56/.223. You would not use a .338 in a home defense but you would use a 12 gauge.
In a home defense situation scatterguns, centerfire rifles and centerfire pistols can not be compared in an apples to apples manner.
If you want relatively light recoil while maintaining payload and power go with a 12gauge and a 2 3/4 loading. Ammo and firearms suited for the task are more readily available than the .410. They are useful for other shooting and hunting tasks.
The .410 requires you to make compromises that I would rather not make in a defensive situation.
And your choice isn't mine sir. I like the .410 because it meets my requirements, and I made this thread to try and help others make their own choice.
My reason for posting the comparison of popular rifle calibers and the three popular shotgun gauges was a way of saying that each has it's place in the grand scheme of things.
Also I don't think you have a full grasp of how much a 12 gauge with "00" buckshot will penetrate in the context of this topic (home defense), in which case I think you might want to do a little research on the subject. There is a reason I propose that #4 buckshot or it's closest available equivalent (#3 buck or #2 buck) should be used in any gauge, and that is to offer a better chance of hitting a vital organ or structure while reducing the chance of collateral damage beyond the threat (notice I said reducing the chance of collateral damage beyond the threat, because the possibility can't be removed entirely).