AAH I've shot a couple .22 LRs. About as fun as a trip to the dentist, IMO. Especially the revolver. Now that the OP says assume this will be the buyer's only firearm, I have to say .22 LR is not a good idea if the buyer's goal is HD. If there are no plans to get a .223 or a shotgun, then I'd have to recommend getting something with enough power off the bat.
Youngda, whether the shotgun is better or worse is not very clear. I actually think the carbine makes a better HD platform than a shotgun, for several reasons. I'll agree with you on price, but as has been mentioned by the OP its not a factor. I would love for you to enlighten me on how I "don't see past my own nose". I'd also like to hear how a rifle is so much worse for a new shooter, when (as has been said in this thread) many people join the Army/Marines with no previous firearm experience and get taught on the .223 M16/M4 just fine.
I take it you're not planning on having kids and grandkids and enjoying shooting with them. You're being very shortsighted about the best way to introduce youngsters and other non-firearms owners to shooting, but possibly that doesn't matter to you.
If someone is timid, I can borrow my Dad's .22s and start them off with that. However, I'd rather start them off on a BB gun and then go to a 9mm. The first gun I ever fired was a 9mm, my friend and his sister first shot my .40, and my Mom first shot a .38 revolver. None of us were turned off by these. You are right, though, I don't plan on having kids.
Like I said, I've shot the .22 before, and my experience is that it is less fun than either a BB gun or a 9mm.