Regrettably, the divers that repeat this joke are often serious. Many divers choose a buddy simply because they are alarmed at being alone, and not because there is a possibility of the buddy actually assisting in an emergency. Unfortunately, few people defending the buddy system seem to address the critical point of whether it does, in fact, make diving safer as intended. Since the introduction of the buddy system 30 years ago, a large body of divers has developed who have made careers out of sport diving. These people must now look to their experience to decide whether or not the buddy system has worked, or whether it should be modified or even abandon.
All diving involves risk.
As soon as you step near a full scuba cylinder you are at risk. And every step that you take getting on and into the water increases your risk. In fact, there is an escalating scale of risk as dives become more complex. In general, the risk of a certain dive is a function of the technical requirements of the dive and the environmental conditions. It has nothing to do with the diver.