A socket outlet is a wild card, none of us can predict what the unskilled or un instructed consumer will connect to it. You have correctly recognised that the CPC is not a benign conductor and it has the ability to introduce a potential difference into an area where a potential difference would otherwise not exist, the same is true of bonding. This is a typical example of the 'Dunning Kruger Effect' when we do not know what we do not know, until we know it. I am as guilty of the next man on this and I have recognised huge holes in my knowledge in the past. I spent half of my working life Lecturing in Electrical installation, my students were well informed and working for some of the best contractors I have met, it is from them that I have gathered my knowledge base, especially in the field of earthing as this is so crucial in the agricultural environments found in Shropshire.