So in theory if all GA craft were equipped with CAPS and pilots were
trained in their effective use, they might cut the number of fatalities
in
GA accidents by roughly half.

Maybe. But it costs weight and money. This means that, for the same
flight, the plane carries less gas, and this is the leading cause of
crashes. One could fly with more fuel stops, this increases the number
of landings and takeoffs (and low altitude flight). Since there's less
money, the airplane might be less well equipped, and the pilot might be
less well trained. This increases the risk too.

Everything comes from somewhere.

Jose
--
A lot of excellent points. Like many of the safety features on cars, I
suspect that it would be essentially a wash in terms of safety--at a
substantial increase in cost.

Peter