When I was involved in assessing runway capacity and safety back in the 1990s, Gatwick was the most efficient runway in Europe in terms of both safety and capacity at a time when the parallel taxiway was not being used as a second (backup?) runway. And it appears from this link it still is:-
https://www.internationalairportrevi...wick-capacity/
There are also a number of single runways on remote ocean isands - Bermuda and Seychelles spring to mind. They were operated safely as far as I remember. Single runways are definitely not inherently dangerous.