Nothing wrong with back-stabbing a receptacle.
They are UL approved and if they were wrong or unsafe they wouldn't be.
You may be [mostly] technically correct, but why do you suppose that after some years of experience with allowing both 12 and 14 gauge to be connected that way, we are now only allowed to backstab 14 gauge?
Those little springs only give you point contact,
much less surface area involved than with any other accepted method. That means higher resistance, which means more heat generated when current flows. Over time, all those heating/cooling cycles are just about guaranteed to deteriorate the connection--leading to even higher resistance and more heat, along with the very real probability of arcing and/or intermittent contact (the spring loses its temper as well).
I long ago lost count of how many switches and outlets I've troubleshot for that problem. Or for that matter, how many of 'em just blew fire out of the wall and nearly burned the house down.
The only reason we're still allowed to do it with 14 gauge is because the lower current levels take longer to do the same damage. I fully expect the practice to be outlawed altogether some time in the next few years.
