For what its worth, I believe Class D around airports that support passenger flights and indeed large aircraft operations is justified.
Unfortunately the GA fraternity always see this as a no go area with a constant instruction to Remain outside Controlled airspace. Which is usually not the case.
I believe Norwich have stipulated in their request that they maintain enough ATCO's in order to provide maximum ability to cause minimal disruption to GA.
Unfortunately the standard of airmanship with GA (in my opinion) has dropped quite considerably over the past few years, with poor R/T and an over reliance on GPS. This has led to airlines requiring the protection of Controlled airspace in order to use the airports outside in class G.
Class D also protects GA that use it. Don't be afraid of it