The prices have gotten quite high lately, but if you can find one get a Walther TPH .22. Very small, slender, clean in outline, reliable, accurate, true DA / SA action, beautiful guns. You MUST replace one too-weak hairpin type spring first, a very simple task.
BTW, I tend to agree with you. For untrained civilians (includes 98% of the BGs we ordinary citizens would encounter), I'd speculate that 98% of the time the mere appearance of ANY gun will have the desired effect. For 98% of the remaining 2%, being shot at or shot with ANY gun will have the desired effect. 98% of the remaining .04%, shot placement would be key. For the tiny fraction left, well if you run up against one of them then your luck is just terrible. We'll let the big bore guys argue about them.
Did I get the arithmetic right?
The Beretta 21 is somewhat thick in cross section, but they work well also and are less expensive, and the prices are jumping fast. The IJ TP-22 is a little bulky and unreliable in my experience, but they are inexpensive and work well MOST of the time. This model is also available on GB sometimes with other makers names on it. The PPK and PP and PPK/S .22s are fairly large and very expensive. The Walther TPH is the class of the group by far.