You are right, it is possible to use the fog lights with only the parking lights and this is good - my mistake and good for Volvo. I don't agree with you that fog lights are primarily to be seen as warning lights. If the fog is so bad that no penetration is possible, fog lights serve no purpose because the car is undriveable, anyway and headlights would be as good as anything for warning. For a fog density where some slow progess is possible, the fog lights are designed to give a low and near illumination to provide optimum visability while minimizing glare. The same applies in driving snow. We seem to have a different concept of fog lights.