This is an old argument. For most of us guys that grew up in the South, a .22 was our first rifle and, for many, our first handgun. Mine was a Marlin 39A, and I first used it to kill rats (big suckers) around my Dad's chicken houses. Dad was a WW II 2nd Inf. Div.vet and he taught me how to shoot. I also squirrel hunted with it and took it everywhere fishing, walking the RR tracks by the river, etc. I plinked at everything. When he bought me my first deer rifle, a Marlin 336 30/30 which I still shoot, he said, "this will be just like your .22 except it will kick a bit. Just hold it tight and do everything else like I showed you." I killed my first deer 2 weeks later... a 50 yd. shot with iron sights. I was a cinch for the HS rifle team. Anyway, I think as a confidence builder and sight picture training a .22 is fine, rifle or handgun.
BTW, that was in the early '60's. My best friend and I, at 11 years old, could pack a sack lunch, canteens, and take our .22's and walk through the neighborhood, down the main drag to the river bridge, go down and walk the tracks shooting all day by the train yard and nobody thought anything of it. Now days, if they saw two kids walking with .22's, they'd call the damn SWAT team.