The whole question of ATS outside controlled airspace is being discussed at the moment, and there will no doubt be a variety of views, with justification.
I am inclined to think that what we need is not more CA, but a known environment. There is plenty of space in Class G airspace, and the RAF seem to manage to make approaches into aerodromes without too many problems.
A known environment can be achieved by several means, including a mandatory radio area (like used to surround Upper Heyford years ago), by all aircraft having finctioning transponders and being obliged to switch them on, or by having a radar flight infomation service, like in France, with a promulgation that within (say) a radius of 10nm of any busy aerodrome in Class E,. F, or G, there is an obligation to call them. Or, better still, an obligation to call the AD concerned, to avoid frequency separation.
In other words, there are more ways to skin this cat than just adding more and more Class D airspace.
All ATCOs familiar with Class D, and users, know that Class D airspace usually ends up an impediment to transiting GA, even though it ideally should not. Not as often as it is, anyway.
But aircraft flying into DSA have to be protected one way or another - simple as that.