And the relevence of this to Mode S is?
As a demonstration of how individuals can dissaffect those who they want to get on side in their campaign. GA needs support from all sides and it would be better for some to realise that they are not the only fish in the pond. The voice of pilots (whatever they fly) will be much louder if people work together rather than looking only after their own interests.
From the ATCO point of view, some form of identification device (whether that be Mode S or not) should be mandatory within Controlled Airspace, whether you are a glider or not. In specific areas, exceptions could be made, by creating Restricted Areas (Temporary) which function under a Letter of Agreement and ensure that only the non transponding traffic is within the area when activation is authorised. In addition, VFR routes where carraige is not required could also be considered, subject to conditions placed on the flight. In Class G, it should be mandatory above FL100 for carraige, since the 250Kts speed restriction put in place for 'see and be seen' is removed above that, making it more important for everyone to be visible electronically. Mandatory equipment carraige zones should also be investigated around major airfields or TMAs, with a proviso that the size of Controlled Airspace be reviewed with a view to reducing it since unknown traffic is now visible.
All that may impinge on gliding, but there is nothing to stop specific local agreements being put in place to provide compromise airspace management and solutions. You won't get unfettered access to all the airspace over the UK if you don't carry the required equipment, but then neither do a whole host of other pilots. What you will get is some airspace sharing, by agreement with everyone who operates in the airspace. Pragmatism works surprisingly well, even if some folks cause you to need a lie down in a darkened room.
Incidentally, the agreements I have worked on with the gliding fraternity seem to work OK from both sides of the house so one bad apple really does not spoil it for the majority. P600 delegation, P600 access, and the Upper Gliding areas were some of the ones I put together.