Picking up just one point - transponder weight - surely that argument is nonsense, given the variation in pilot weights, and the huge increase in the average pilot weight during the certification lifespan of the average glider.
I am 77kg. 12 years ago I was 71kg. 6kg is one helluva lot of hardware; my entire KFC225 autopilot system (1 computer, 3 servos, other little bits) might weigh 6kg.
Loads of pilots are 100kg...
Under EASA rules we can only fit a transponder in accordance with the manufacturer's approved scheme. There is no such scheme for most gliders.
I genuinely don't want to start yet another 'transponder' thread but if I was flying a glider I would buy a Mode C transponder and install it, and to hell with silly rules for certified aircraft. I can legally install a Garmin 530W in my Toyota... maybe not a transponder (in the Toyota; it would be 100% legal to install but it would be illegal to make it radiate). This would make me visible to many others, and might just save my life one day. Remember: Class G is Class G.