It's a good idea in principle, but in practice? Even NL, DK and DE don't have cycle lanes on all main roads.
But go there and take a look. Or better still, have a cycle around and a drive around. It's not just about the cycle routes - it's about where they are, where they go, how pleasant they are to use, and how well-maintained they are.
Yes, there are some roads where there's a cycle route and where you're not allowed to cycle on the road. But the routes are good enough that there's no earthly reason you'd want to. Equally, clubs riding in packs and roadies spin along on the roads and no-one cares or minds.
The questions about space, cost and so forth were just the same in those enlightened countries, but there was the political will to make them happen anyway - sometimes against resolute opposition. And they're used, and as a result everyone rides a bike sometimes - or knows someone who does. So cyclists aren't an out-group as they are here - they could be your mother or cousin or the girl next door.