My 2ps worth.... as a Controller and a Pilot.
Nobody so far has mentioned the phrase Duty of Care. Now, this may not mean anything to most GA pilots but is very much on the mind of ATCOs that ply their trade in class D (and E to G) airspace in the UK.
So what's is all about? Lets assume in an ideal world that GA is granted largely unfettered access to a Class D CTR, with appropriate traffic info and routings exactly as they want.
All well and good for a large number of well briefed, planned and executed VFR flights. Unfortunately some VFR flights are not so well thought out, or flown.
One day one of the "not so good" VFR flights enters class D, and gets it all horribly wrong and ends up very close to an Airliner with 130 souls on board. Avoiding each other is a joint responsibility, but at say 160kts and focused on the ILS the poor old B737 crew don't stand much chance of avoiding the non SSR equipped CUB wandering through the final approach track...... But hey, it's class D and it doesn't matter right? See and avoid, yeah? err No.
So, who's in the dock afterwards? You might well say that "Well, the ATCOs in the clear, he gave traffic info". Except that a barrister will not see it that way, nor will the relatives, nor will the public. They WILL see "130 people endangered for the sake of a joy ride" type headlines. And they may be right.
You see, ATCOs have a "Duty of Care" to all their charges, be they IFR or VFR, wherever they are. It may just be SAFER for the VFR flight to avoid class D airspace, due to the type of traffic in the CTR. The ATCO might just be doing you a favour.
It's already been stated that most Class D CTRs in the Uk are quite small. In my own (flying) experience routing around them doesn't add much time to my route, and the navigational challenge isn't beyond most PPLs, even me.
Oh, just one more thing. Fuel duty. As far as I'm aware NONE of the tax on AVGAS goes to the ATC providers at various class D airspaces in the UK, and the MoD picks up the tab for LARS. You get a VFR transit for FREE. ATC services are paid for by arrivals, be they IFR or VFR.
In the USA the FAA funds ATC (via the government). Airspace there is seen as a National Asset, available to all and funded accordingly (nowithstanding the latest FAA budget deficit). This isn't the case in the UK.
Well that's my 2ps worth. Feel free to disagree, argue the toss, whatever.... life's too short etc etc
Rgds BEX