Different strokes for different folks. When turkey populations are below desired levels it makes sense to protect hens during the hunting seasons. Turkey pops in many Midwestern states, including SD are are very high right now and in many cases still expanding. As long as populations and harvest levels are properly managed, there is no reason why people who wish to shouldn't be allowed to harvest female birds. The issue of whether or not hens should be legal targets seems to me to be more of a social regulation. The fall hunting tradition (where female birds are fair game) seems to be more accepted in the northern states, while southern states seem to be opposed to the idea. This may be a reflection of turkey history in these areas? Southern hunters may remember the "lean times" when it was rare to hear a gobble, let alone kill a bird (maybe it IS in your DNA CutNRun, or more accurately in your hunting heritage). Many hunters in the Midwest never experienced this, as there were no turkeys to hunt during this period, all they've ever really known are rapidly expanding populations.
The idea that killing an "egg layer" is sacrilege has become ingrained in the hunting culture. It makes sense to hunters that more hens = more eggs laid = more turkeys. While sometimes this is true, in many cases reality is much more complicated. The number of breeding age hens in a population is rarely the bottleneck for game bird recruitment (not to pick on you TJ, but in this respect the SD regulation is probably more FORWARD thinking than backwards). Habitat, predation, and weather typically play a more important role. In some cases more breeding hens can lead to lower recruitment through competition for quality nesting sites and food resources, as well as supporting larger predator populations.
There are many other examples of social regulations. Doesn't Mississippi prohibit the harvest of jakes during the spring season? Hen pheasants are another good example, there is little if any biological support that protecting pheasant hens during the hunting season leads to higher pheasant populations in following years. It wasn't too long ago that people thought shooting does was about the worst thing going for deer herd management. Popular opinion changes slowly on these issues.
My point is there are many different ways to successfully manage a turkey population, depending on the particular goals of the state and agency responsible for that management. Protecting hens during all seasons is a perfectly legitimate regulation if it is supported by the hunting community that regulation impacts. By the same token, if the people of SD want to be able to shoot hens in the springtime, GF&P can figure out an acceptable harvest level and let them have at it. I think respect for the hunting heritages and traditions of all is always a good idea. When in Rome...