I'm with Stuart. While the overall numbers of diversions may be small a reasonable number are caused by pax not putting their hand up and saying I'm not well enough to fly. There was a very recent example I was involved with whereby it turns out the pax was swallowing prescription pain medication prior to boarding and once underway the acft had to divert to offload the pax to hospital with a pre-existing medical condition. Why should the airline have to bear the cost of that?