Obeying road markings is not all that's required of road users. If an overtaking bus's left wheel is 1" to the right of that white line, and a cyclist's wheel is 1" to the left, both are within their boundaries, but in that case the bus is going to hit the cyclist. In such a situation, the fact that the driver was fully within his lane does not mean he wouldn't be guilty of an unsafe pass. The law requires not only that road users obey lane markings and traffic signs, but that even if they are doing so, they must not endanger other road users. And sometimes, the law even requires that road users disobey such markings, when obeying them would cause an accident. No one can just blindly follow the road markings - if they did, thousands more people would die on the roads. I mean, surely this is kindergarten stuff! It's not something that sane and intelligent adults should even be debating!
A cyclist is not a 'muppet' if he doesn't cycle fully within such a narrow lane. Often such lanes are filled with dangerous debris that can cause a fall, so cyclists must avoid such debris, which often means cycling at the edge of such a lane or outside of it altogether. Overtaking drivers have the legal duty to pass with a safe margin. The idea that a driver can just overtake a cyclist with the tiniest clearance whatsoever, as long as he's obeying road markings, is ludicrous! Such a notion has no basis in traffic law because it is inherently deadly.
As for cyclists obstructing traffic by using the general traffic lane, this is nonsense. A cyclist going at a normal cycling speed cannot possibly obstruct traffic. There is no right to a certain speed on any roadway and road users in a queue of traffic must respect the lead vehicle's right of way - the road is his.
As for bike lanes having been put there to make cyclists safer, I can show you ten studies that show that they decrease safety for cyclists. Your attitude seems to be mired in anti-cycling and inferiority-cycling propaganda.
Road markings are guidelines that are meant to enhance safety. But they do not guarantee it. The only thing that guarantees safety is an alert and careful road user using his brain. If he just relies on road markings to do what his brain should be doing, he'll kill someone and he'll end up in jail, because the law requires much more than that.