Because there is no rimfire .22LR ammunition that matches the reliability, muzzle velocity, penetration, expansion, or energy of quality centerfire 9mm, .40 S&W, .45ACP, 5.56 or .223 defensive ammunition (etc.) There just isn't.
****Some High Velocity 22 have more FPS then some of those pistols rounds.. Yes we understand they aren't as powerful that's a given..
Then why bother with an actual firearm for defense? Why not just cut the orange end off an Airsoft gun and save yourself a lot of cash?
****Maybe because an airsoft gun isn't a firearm and having a bullet available is a safer option. Many people have deterred intruders, muggings by just brandishing. Nutnfancy on youtube has a whole video about what happened to him.
You're recommending we bet our lives and those we love on what an armed intruder might do? That can be your plan. My plan is to put him down as quickly and surely as possible, not scare him into going away.
****My plan is getting my 9mm for because of reliability like you mentioned and I agree with, but this thread ISNT about 9mm or any other caliber that many have mentioned, its about a guy who wants an opinion for his 15-22. I knew my points would get flack but they are valid points for his particular case concerning question he asked.
None of them do, until one does. But that's not the important thing. Adequate penetration through heavy clothing, fat, muscle, and bone to reach a vital organ or a critical CNS component is.
****HV 22 goes through a 1/2" plywood at 300 yards.. Youtube
People who care about their own protection and the protection of their loved ones, and who understand the basics of terminal performance, yes.
****I care, and understand performance but once again this is about the 15-22 in a HD scenario. Not anything else.
I thought all you had to do was show them something that looked like a gun and they'd faint on your living room floor. Which is it?
****Look at glocks new commercial with the hot girl, that's exactly what happens

And it depends on the situation, if a guy is walking out with my tv the first thing I do isn't going to be "putting him down". But if he was armed lets say with a crow bar with intent to hurt me then taking a shot seems more reasonable.
What we are saying is, there are far better choices for a defensive firearm and caliber than the 15-22 in .22LR, and the strawman arguments are getting tedious.