I cycle in a city - Bristol, and I meet lots of others doing the same. Yes I saw a prat of a cyclist today, shouting at a pedestrian to get out of her way (pedestrian 3/4 way across the road and cyclist could easily of gone around her), equally I saw lots of sensible cyclists. Just like I see sensible cyclists and drivers every day. Doesn't mean that you don't get stupid ones in each group. Just the stupid ones in cars can do a lot more damage than the stupid ones on bikes. I also saw a child cycling on the road to primary school on their own today, are you saying they need to have insurance etc and 3 day course?
I don't mind doing a test every 5 years on my bike if the same test is brought in for all car drivers? Mind you there would be a significant cost involved and lots of drivers not passing of course but that could be good.