I think that the right for people to NOT carry transponders / radios / whatever should be preserved if they really want.
However there has to be some give and take and I'd be happy to have mandatory Mode C (as a minimum) above say 3000' AGL, and Mode C vales around big ATC controlled airports which don't have Class D airspace attached (Exeter / Plymouth for example). If you want access inside this mode C area, obviously you need to have it turned on to Mode C or better unless previously agreed with ATC.
Isn't this fair enough? The the microlight lobby can go on flying without one, gliders can as long as they stay below 3000' and no one has to dash out and spend any money on a txpdr, and we don't suddenly see new airspace popping up everywhere.....