Let me tell you how primary lane travel works in civilised countries: drunks and the others you mentioned end up in a canal, stranded up on a meridian, or crashed into a bollard.

That's because they do more there than just say "share the lane" and call it a day. They narrow the road to almost exactly the width of a typical car using unforgiving barriers like bollards, medians, and 5m deep canals. They restructure the roads so they aren't straight throughways, but brick-paved, winding pathways through the city.

They turn roads into obstacle courses, calming traffic, because as we all know, drivers may not be worried about killing cyclists, they're horrified by the idea of scratching their paint.

They still have drunks of course, but they're typically on bikes (since driving is so impractical), and they too often end up in a canal.

Here's a decent example from Amsterdam where they effectively have 3 classes of road:

• Highways where no bikes are permitted but there are always entirely separate cycle path options to travel the same distance.
• Wide through roads with level asphalt paving and typically a curb, a row of trees, a tram, or other safe barrier between cars and cyclists.
• Narrow, often winding shared roads where traffic is naturally calmed by the terrain: bollards, canals, bricks or cobblestone, big speed bumps, raised crosswalks, or other oncoming cars in a space clearly designed for a maximum of one. Even the traffic lights here are configured to reduce speed by defaulting to red in all directions.

That last category is the majority over there, and a big reason why the city is so safe and quiet... unless it's King's Day or New Years eve. Then these spaces are flooded with loud, drunk pedestrians or children shooting fireworks at random. On those days I recommend trips out of town ;-)

It really doesn't. See my other comment here for more detail.