As an undergraduate I recall various experiments we did in a zoology classes, looking at how animals respond to stimuli. One simple one is surprisingly salient to cycling. You get a bit of glass and some snails. You let the snails start wandering around on the glass, and then you bang on the other side. The snails all quickly retreat into their shells, because obviously there's something dangerous happening. You can time how long it takes each snail to re-emerge and go about its slimy business.
After a time, you knock on the glass again, and time their re-emergence again. After a few cycles, the snails are used to the noise and come back out far faster, some brave gastropods even daring to continue on their paths with little more than a flinch.
Animals, whether its a snail or a stupid monkey like me, can be conditioned into ignoring some danger. Consider, for a moment, someone swinging their fist at you - you'll flinch, back off, and probably put your hands up and defend your face. Its really hard not to. Go on, try and walk face first into the side of a door - you'll stop yourself. But a boxer, by fist-fighting frequently learns now not to flinch, how not to turn away defencively, and continue looking for a way to counter-punch while maintaining a level of defence. We can be conditioned to take a certain amount of risk and to suppress our natural instincts, to fight off the reflex loops that take us away from danger.
People who still maintain that cyclists must be trained to ride assertively in traffic and that cycling facilities run counter to good cycling practice and breed poor cyclists aren't really arguing for 'training'. They're arguing for 'conditioning'. Snails on a window have not in any meaningful sense been trained, they've been conditioned such that the association of risk is slightly ameliorated. But its not a particularly pleasant process for the snails (or the bored students), in fact its really quite frightening for the snails. A gastropod wouldn't choose to repeatedly face something instinctively life threatening until its instinct to duck back into its shell is repressed.
So you're an advocate of cyclist conditioning? You want to tell those too scared to ride that they've got to ride in a way that is counter to their perceived common sense, further into the road and assertively such that they're closer to the source of risk (i.e. cars and lorries) until they no longer flinch back to the gutter every time one passes? That isn't going to work. Very, very few people choose to be conditioned to accept something instinctively terrifying. Telling people to harden up to fear isn't a route to mass cycling - its why almost no one in the UK cycles. People will retreat back in to cars rather than face terror until it is no longer terrifying.
Do you advocate that vehicular cycling is the route to a cycling utopia in places with low cycling uptake? Then you're ignoring the basic biology of all animals with the ability to get up and move. Including humanity - this isn't just human biology, it is innate behaviour across the animal kingdom. In other words, you're wrong. Fundamentally, biologically, and entirely.
The only game in town is good, safe, segregated infrastructure. Just get with the program.