My point here, though, is merely to observe with a chuckle and a shake of the head, how these threads almost always result in most posts advising people to go for the most powerful round and, yet, it is easy to find other threads going on simultaneously where people suggest all kinds of things for their wives, mothers, aging fathers, etc., etc. and seem quite comfortable suggesting these people carry .32 acp, .380, .38 special target wadcutters, and so on.
These "caliber" discussions are a lot like discussions about religion or politics -- lots of opinions, some strongly held, but most of the opinions offered with little supporting facts or evidence, one way or another. It's clear as a bell and any fool can see that X is right....
There's quite a bit of data available about the effectiveness of the larger calibers, but we've not been able to find evidence about the smaller calibers. Some folks seem to feel, for example, that a hollowpoint is a hollowpoint, regardless of caliber -- i.e., it will open up as expected, and do more damage than a FMJ. Others claim, with equal assurance, that FMJ in the smaller calibers are the only way to go, because HPs won't open up from those small, underpowered rounds.
When I picked up my first "pocket gun," a Kel-Tec P3AT, I believed that a HP was a HP. Since that time, I've been looking and looking for facts to support that belief that these smaller calibers will do the job, and simply haven't found it. Haven't found evidence that they WON'T do the job, either. Unhappily, the lack of evidence is not evidence, and there's remarkably little available for either side of the argument about these small calibers.
Why do people suggest these unverified/unproven things for their friends, family, etc.? It's because people often do dumb things, believing they're smart things, and there's not a lot of data around to make it clear that those things are dumb -- or smart.
As for the assertion that one should use the biggest caliber you can handle -- there is a fairly large body of data available about "results" when using the larger calibers, and little available for the smaller calibers. So, for some folks erring on the side of the calibers with "better than no information" seems to be a pretty sensible rationale.
I remember when I bought my first big gun safe, the guy I bought it from told me, "buy the biggest safe you can afford; you'll regret it if you don't."
I didn't, and I don't really regret it -- but I could sure use a larger gun safe, and they cost a lot more, now. Some advice is just common sense, but my pocketbook didn't recognize it for what it was.