Chippy, the answer is.....money, as is often the case in aviation.
This option has been considered a number of times before, at least a decade ago, during my time as a chief pilot at a police ASU.
After one rescue by a police aircraft, where an observer went out on the skid to pull someone from the sea, (albeit successfully, IIRC) we received a circular letter from the CAA, warning pilots that in future they may be prosecuted for endangering the aircraft if this happened again! Not sure the final outcome, I'm certain most of us decided to treat it with the contempt it deserved.
Not sure how an unconscious person would get himself onto a long line, btw. The CAA certainly don't generally allow persons to be dangled / suspended from a long line, see above! I know one pilot who was prosecuted after a load handler inadvertantly flew with his underslung load to its destination.....