For me it's about perception, who people identify with and how they respond to what they do.
I'd like to see a lot more people reconsider the role of the car in their lives and society in general, which I reckon/hope would lead to things like: People in cars not seeing cyclists as annoying irrelevancies, less school runs being done in virtually empty 4X4s, town centres being dominated by people instead of cars, etc etc.
IMO the views of 'the middle' are key to this. Most folk are more-or-less decent, reasonable people, and I think they're more likely to consider their own behaviour in light of the behaviour of other people that they identify with and have some sort of respect for.
So they're more likely to wonder if they should give cycling to work a go after chatting to Dave down the corridor who bikes to work every day and seems like a pretty normal bloke, and maybe more likely to wait a few seconds extra for that cyclist to pass the junction before pulling out when they're on their way home.
I think they're less likely to identify with those crusties on tall bikes, or those twunts in tights who blow through the lights every day while everybody else waits, or that Critical Mass lot who made a point of trying to ride down that road that they knew they couldn't because the Olympics is on, FFS. Cyclists? To$$ers.
Anyway, that's part of my take on the whole 'road manners' vs 'I'll do what I like cos I can, and anyway everybody else does it' thing. Hopelessly naive maybe...