I beg to differ. True, many fences are easily overcome by adult humans, but most fences are not designed with adult humans in mind. Most fences are intended to keep animals in or out of an area. In more urban areas that may extend to small children. In high security areas, fencing may be just one layer of security, but it is certainly more than just "suggestive". In any of these cases, the fence is useless if it has a gap that can be exploited.