in England, even roads with a "central white line" are almost universally only wide enough for a single car at a time to drive down them by any sane measure. When there is no white line, cars will often drive down the middle of the road, and "slow down"/"move over" when another car approaches, entirely out of necessity.
When there *is* a white line, most cars won't do this, despite the same necessity still being there.
England's roads (the ones they are talking about) are basically foot-paths which were widened over time enough to allow horses through, but which were never widened or maintained enough to allow multiple cars through in any case. Two American cars would literally not fit side-by-side on these roads.
What is actually needed is wider, better-lit roads, with real shoulders and barriers at the side. But that costs money, so instead we get proposals like "what if we don't bother to even repaint the lines anymore?" and "people will slow down if we stop lighting the roads entirely"
As for "slowing down", the speed limit on most roads (even ridiculously tiny roads) is "meh, whatever". If they really want people to slow down, reducing the speed limit would be the *first* thing I'd try. It seems not to have occurred to anyone in England, though.