When speaking to the power of the .22, I always reference a little test I did to see if there was any difference between round nose .22 cartridges and hollow points. I noticed a lot of the .22 LR bullets had an incredibly shallow depression in the nose, which I figured would translate to very poor expansion/explosion (for lack of a better word).
For the record, it was the Remington Thunderbolt bulk .22LR. Not exactly high-performance stuff.
So I filled two aluminum cans with water and set them on a fencepost. I shot the first one with a round nosed bullet. The entry hole was ~1/4 to 3/8 in. in diameter and the exit was ~ 1/2 in. in diameter.
The second can was shot with a hollow point .22LR with a light depression making the distinction. I don't think it was even a millimeter deep. I shot the can from about 25 feet away out of an 18 in. barrel. It blew the can into about fifteen shards with the top of the can and the bottom barely holding the scraps together. At fifteen years of age and with limited shooting experience - the result left me slack-jawed and wide-eyed...surprised to say the least.
That was when I realized how much energy a traveling bullet carries in equatable terms - not to mention how important bullet choice is for its chosen role - even if it is only a .22LR. The un-scientific test added a significant amount of understanding to an already healthy respect of firearms and the reasons we should follow very strict handling rules.
I just kept thinking, "It's a .22LR for goodness sakes!" Translate that release of energy to a .30-06 or even a .30-30! When punching holes in paper all day and trying to make a comparison to a cartridge's effectiveness, I can see how people can get overly concerned with bullet diameter, etc.
It is also hard for us to grasp the difference in cartridge/bullet effectiveness when the only examples most of us see in person of something being shot are limited. Honestly think about how hard it is to measure how "blown up" a cantaloupe, apple, or a soda can get in terms we can see for ourselves.
But if you take a round like the .22LR, which garners little to no respect in the selection as a defensive round (due to the relative difference in energy to other selections) and conduct a demonstration such as this, you can help people understand the issue and choices in tangible terms.
If you are trying to get a good idea of how much energy a round carries, I highly recommend finding a farm or other piece of land you can shoot whatever you please vs. just paper. It is a very effective (and just as important - easily/cheaply done) demonstration for both new shooters and guys who have been around a while. It highlights the need to respect firearms, no matter if it's a squirrel gun or the latest hand-cannon. It also demonstrates the important of bullet choice, not just cartridge size.
I worry, since people are usually only reading/comparing numbers and other's opinions, their lack of personal experience limits the ability to make informed/effective decisions based on the information presented.
Therefore, most of the arguments presented in such threads are academic. We do not see, in clinical terms of tissue damage, the results of the other ways in which bullet energy is measured. It's all a bunch of numbers on a piece of paper or a web page. Therefore, we only have an abstract understanding of the issue at hand.
Not only is it abstract to us, but without seeing results in numerically significant examples, there are very few "experts" who can make informed choices and statements on the issue also with significant accuracy. I would think that the most respected and educated person would be a surgeon who has been through a war, has operated on an incredible amount GSW, and was able to compare that to the numbers we constantly pour over to select defensive cartridges and bullet types. Even then, he would probably only have a baseline which to compare to since most battlefield GSWs would be from the predominant cartrige of the enemy's choice.
We "have" to err on the side of severe overkill when choosing a handgun or rifle. The stakes are too high when considering a failure in the area of self-defence. I believe this is why most people do so, even if a .22LR is adequate enough to kill or maim someone to interrupt an attack in many situations.