When it is busy, our IFR traffic is quite simply at risk from Joe Bloggs Muppet in his light aircraft telling me he is going from A to B via C nowhere near me. Inevitably this happens when two light aircraft wanting to actually enter the zone to transit. The life story from Joe Bloggs means that the first two are unable to get cleared in (there is only so much RT time). So who loses out, the despondent 1 and 2 who end up saying "going around now"??
Looking at this slightly differently, is it acceptable if transits are regularly refused because of controller workloads rather than because the airspace is full?
Presumably when an airport requests controlled airspace they must be able to demonstrate that they have sufficient controllers to work all aircraft arriving and departing, and all aircraft wishing to transit, or alternatively to fill the airspace to safe capacity, which ever is the greater. This is an assumption on my part, and I'm open to correction, but I'd be surprised if it's wrong.
Why then doesn't that airport have to ensure that there is sufficient controllers to deal with all aircraft wanting to use the airspace in the following years? If the airspace is there, then in my humble opinion, it should be staffed sufficiently.
There will always be unusual occasions when everyone calls at once, and it's simply not possible for the controller to deal with everyone. But when this becomes a regular occurrence then it needs to be fixed. Fixed by getting additional controllers, and additional frequencies if necessary, and not fixed by saying "Remain outside of controlled airspace" to traffic wishing to transit.
Airspace being full to safe capacity is a different matter of course.
dp