Having spent a large part of my life living in Devon (a very rural part of the United Kingdom, lots of farms, tiny villages, small roads/lanes - often not wide enough for 1 car in each direction, except at specific "passing places" - with high hedges to the side limiting both long range visibility of the road ahead and the run-off/avoidance options for traffic coming in the opposite direction), I can say that driving on a road with no central line marking, which is also narrow and with limited visibility, does tend to lead to either slower speeds (the careful drivers) or much higher speeds (the drivers who fantasize about being a rally driver, and who assume nothing will be coming the other way).
Take away the line down the middle of the road, and the road feels narrower, at least to me. But there may also be an assumption that the road is a (very wide) one-way street, so the result would be that drivers move to the middle of the road. That would make life interesting if you come around the corner on such a road, and see a car driving in the middle of the road. Maybe I am not giving my fellow drivers enough credit, but when my father taught me to drive, he always reminded me "assume every other driver on the road is an incompetent idiot with no control over their vehicle"... sadly I have seen a lot of evidence that backed up his statement.
Another element came when driving the E10 highway in northern Norway and Sweden with my girlfriend (very competent driver, in a landscape that was sometimes the typical alpine "wall of rock on one side, sheer drop down the other"). She was perfectly happy and capable of driving when there was a line in the middle of the road, even with large semi-artic trucks coming in the opposite direction at 80+km/h (50+mph), but as soon as the lines disappeared because the road narrowed a bit, or there was a stretch of newly resurfaced road with no markings, she was very uncomfortable and wanted me to drive, because the road then felt restrictively narrow, especially with the trucks driving on it (there was space for the truck plus our car, but not a huge margin for error in car positioning).