I haven't cycled into central London to work for many years now but often have to drive in and out. Yes, there's bad driving and riding on both sides, but to give an idea of why so many have a downer on cyclists, here are my observations from just one short leg of a journey in this afternoons rush hour.
At cyclist coming towards me from opposite side of a crossroads who was chatting on a mobile phone, makes a left and all the way to the next lights and who knows where one handed still chatting.
A minute later, I overtake a lady well in front of red light cross roads. She rolls up my inside through the stop line, sees that the traffic crossing us is stationary, then swings a left straight through the pedestrians crossing on the green man.
A mile down the road, ladies ambling two abreast swinging out past stationary vehicles etc with not a look or signal or a care in the world. Only went to single file to get up the inside of queuing traffic before resuming two abreast in font of said vehicles.
Within another mile, three kids (teenage at a guess), all on one bike riding on the wrong side the road against the traffic (as in opposite kerb).
Why post? Admittedly they may have been 'fair weather' non-commuting cyclists this afternoon, but they were a let down. I see enough bad with the commuters too to understand both sides of the argument.