Hello Dave,
Your analysis of the situation relies on the hypotheses that all drivers are also cyclists - which is not true and that cyclists change their road habits when they drive a car. Of course there are a vast range of different behaviours displayed by both drivers and cyclists, some good some bad.
On balance I do think the standard of driving has changed vastly from when I started. But that is partly due to the big increase in the numbers of drivers, so our roads especially in urban areas are far more congested. But all area's have in my view seen a general deterioration, and many illegal activities, Speeding probably the most common, failing to signal intentions, parking half on pavements, poorly adjusted headlights, .................... etc. etc etc.
One aspect which must be a contributory factor is how the performance of vehicles has increased model on model, family saloons to-day can often have top speeds of well over 100mph, where as cars in teh 1960's often could barely reach 80 mph. We are now faster accelerating and braking harder than older cars. We may have more and better safety features, but has that become a reason to drive more aggressively?
Some cyclists are also pushing the boundaries, as has already been pointed out some don't respect traffic lights, or even one way systems. They also weave in and out of slow moving or stationary traffic with little regard for others, But before the motor cycle brigade start to tell us they are trained to weave, the one aspect they fail to include in their rebuttals is the consideration of when it is safe to do so, and when it will not impede or adversely affect other road users.
We are all road users and must consider all the others involved, it some who think they are above sharing, and decide to ignore the safety of others who are the ones that need to consider their actions.