Firstly I'm with Mary Meager. This is topic initiated by Professional Pilots to try and enhance the safety of Professional aviation. Why it was demoted to Private Flying is a mystery; and then further demoted to Questions which is listed under Ground Ops & Other Forums. The Mod's have it wrong if they wish to allow this debate to bear fruit.
Regarding the gliders and lookouts: of curse we all should and the vis from a glider cockpit is excellent; but out a glider in a thermal and then ask where is the focus of the pilot? Round & round and looking mainly into the turn and concentrating not to lose that precious lift as YOU CLIMB. Meanwhile the jet pilots are looking out, just having popped out of cloud, and are DESCENDING. The glider will be invisible, out of sight. And notice how gliders are often nice clean creamy coloured and very sleek. They were stealthy before the name was invented.
There is the old story of a Chipmunk doing aeros and making a 'clearing turn'. They pulled up for the loop and looked down on a jet flying through the middle of it. It was not visible during the clearing turn. Even big jets are not 'instantly' visible from a jet cockpit; you need to know where to look and they employ a correct search pattern. It takes training & it takes time. You then need to assess if there is closure or a threat. You need to assess if the target is maintaining altitude & heading, all while you are circling in a thermal. Been there, done that, not easy.
It does seem strange that is some aspects of daily lives, when the public identifies, or even just perceives, a threat to general safety there is a clamour for preventative action. I know it is not always justified and often too much overreaction to sensational hype. At least the topic is discussed and evaluated.
As a profession we are mindful to take preventative action in many circumstances. Being reactive is sometimes an only choice and then we evaluate if we could have 'seen it coming'. Protecting commercial aviation & pax lives seems to fall into that category. Allowing Class E airspace to continue where it is suitable seems OK. Allowing it to continue where it is not and the threat posed is too high seems to go against the basic principles of reducing a known threat and being preventive. Aviation of any kind is always going to be full of threats. the only sure-fire method is to ground everybody; the death of aviation. No-one is advocating that, correctly; so the task is to find a way in which all participants can enjoy aviation in a safe and reasonable manner.
Hence the call for a learned debate at high EASA level with input from exports of all quarters.