I've seen this posted quite a few times, and IMO it's rubbish. It's almost always possible to cycle out of the door zone, and given that it's one fo the big causes of KSIs (killed and seriously injured), it's not one you should ignore. You're perfectly entitled to ride in the road in the middle of the traffic. If you can't cycle out of the door zone, then I'd want to be going at less than 5mph.
Here's a hierarchy of road safety to follow:
My safety
Your safety
My convenience
Your convenience
My safety comes at the top for riding out of the door zone, and the drivers' convenience in waiting behind me comes at the bottom of the list. That said I'll often pull left as soon as it's safe to facilitate an overtake. Share the road after all.