ProfChrisReed, I'm sure you were referring to VMC flight but how is your lookout in IMC? How do you give accurate position reports when you can't see the ground and does your situational awareness get better or worse?
Unfortunately, your suggestion for a common frequency for all GA too is flawed simply because I think you underestimate the number of IMC aircraft in Class G. I'm sure it would be chaos and achieve little purpose because everyone would hear transmissions from the opposite end of the country. Try listening to 122.7 at Sywell or Compton Abbas - allocation of the same local frequency causes aircraft operating at those two airfields to hear circuit calls from those at the other, 100 nms away. The R/T would be full of crossed and missed transmissions. In addition, IFR/IMC GA is most often going somewhere in CAS, and most often requires a mandatory ATC clearance in order to do so. ATC must be communicated with, even in Class G.
The risk of IMC mid-air collision has long been considered by GA. Many companies require their aircraft to obtain an ATC service using ground-based radar whenever possible.