A few more points for discussion...
First off, we're talking about using the bayonet for personal defense "fixed" (mounted) on the rifle. Right??? (and, in your home)
IF the bayonet is not mounted on a long arm (rifle or shotgun) and you use it for self defense, then its the same as any "knife" /edged weapon, legally, isn't it??
I cannot imagine a plausible situation where I would be defending myself with a rifle with a bayonet fixed, other than I already had it in my hands in that condition when I was attacked. I seriously doubt that I (or anyone) would take the time to fix the bayonet as they were being attacked.
I suppose that, if the rifle were on display with the bayonet fixed, and it was the closest thing I could grab when an attack started, I might grab and use it, but IF that were the case, (and that's bloody unlikely, mate! ) I wouldn't have to face the dreaded question of "why didn't you just shoot him?", Because A) the rifle on display wouldn't be loaded, and B) it is no longer legal where I live to display a functional firearm, if it is functional, it has to be in secure (locked) "safe storage".
SO, if I were ever in the truly bizarre situation of having to use the bayonet fixed on the rifle, it would be because I couldn't shoot my attacker, and had no other option.