They're probably not bad people per se, but so what? I've had people justify a close "punishment pass" on the basis that my lights were illegal (because one was a flashing light, legal since 2005, and actually mentioned as "permitted" in the current Highway Code). The difference here isn't so much that people can't be bothered to keep their knowledge up to date, so much as them not seeing why they shouldn't take out their frustrations on others. That's bad when all you have between you and them is a layer or two of performance fabric, and possibly a polystyrene hat.
I daresay motorists in France and Belgium are as ignorant about current traffic law in their countries, but it doesn't seem to lead them to the conclusion that they'll whizz past an inch off the cyclist's elbow[1] if they think that the cyclist is in the wrong (so far as I can tell from my experience there, at least).
It's also worth restating that primary has a twofold benefit - firstly, it forestalls the dangerously close overtake, secondly, if that overtake happens, you have room to escape into. If you're already in the gutter, you're more likely to be offed, as I found out to my cost after a driver clipped my bars and left me lying on the pavement[2] during my first, abortive attempt at taking up cycling.
[1] Although I'll grant you that they seem to harbour an intense and obvious dislike for their fellow motorists.
[2] Handy, as it allowed all the following cars (I think four or five, although I was too dazed for keeping count) to breeze on past my prostrate form, as I'd not fallen in the carriageway.
