Would it be a great imposition on the gliding community to stipulate that flight in cloud is either carried out with a working mode C/S transponder OR in receipt of a service from a radar-equipped ATC unit? That way, at least other aircraft can be warned of their presence and kept clear of the aircraft (or area if a reliable return isn't being received). Obviously this isn't a perfect answer but it seems a reasonable compromise which would work fine in the vast majority of cases and would mitigate the accusation that other's lives are being gambled with.