Interesting that we are having this debate at all.
If I'm working in the centre of Bristol I have the option of the traffic free Bristol Bath Railway Path - meandering 17 miles or 14 miles on A4 (not that narrow, mix of NSL DC, 30, 40).
Very rarely I use the A4 (normally when I'm late and it's daylight etC). However there are plenty of folk who do and I'd uphold their right everytime. I'd have cheered this guy for being brave enough to uphold our rights!
It's interesting too that you think they've "held the traffic up". In the case of my commute, yes there may be a queue behind the cyclist but all people are 'speeding by' is doing is getting to the back of the next queue quicker. Door to door over the whole 14 miles it's quicker by bike.
I can see a worrying trend here. Ok a different case (not many people commute by horseback!) but there are a number of roads round here that people used to be able to horse ride on that have been made unrideable by the actions of motorists. As already said, it is not the cyclist who is being dangerous it's the actions of a minority of motorists.
If you feel you have to avoid these roads at certain times, how long before you are forced to avoid thses roads at certain times?