A session worth attending is one where something unrecordable happens

The most robust defence of the room is to put something in it that a file cannot hold.

If a session consists of a person transmitting content to a silent room, then the recording is a near perfect substitute, and arguing that people should attend anyway is arguing that they should choose the inferior version out of loyalty. That argument will lose, and it probably should. The recording is more convenient, can be paused, can be revisited, and does not require a commute. Convenience wins when quality is equal.

The response that actually works is to make quality unequal. Ask people to attempt something and be wrong in company. Run the discussion where positions get tested. Do the thing that requires reading the room and changing course. Give feedback that responds to what a specific group has just misunderstood. None of this survives capture in any meaningful form, because the value is in participation rather than in observation, and a viewer watching later is structurally a spectator.

This is a demanding standard and it is worth being honest about that. It asks more preparation, not less, and it does not suit every subject or every stage of a programme equally. But it has one substantial advantage over the alternative: it does not depend on withholding anything. It does not require making the recording worse, delaying its release, or restricting access as a lever. It competes rather than coerces, and the sessions that survive that test tend to be better sessions by any measure anyone would care to apply.