Anyone flying in uncontrolled airspace should be capable of seeing and avoiding other traffic, regardless of speed.
That's not the way that airspace is designed. The whole idea of uncontrolled airspace is that you can fly IFR in IMC in it without an ATC clearance. It relies on the low density of aircraft flying IFR in IMC to keep the risk of collision acceptable.
It could certainly be argued that anyone flying
VFR in
controlled airspace should be capable of seeing and avoiding other traffic, regardless of speed. (Those who cannot should be IFR and separated from each other by ATC.) DAP's faith in this principle can be examined by looking at the ratio of class E to class A airspace in the UK.
However, those rather abstract principles need to be tempered with a rather more pragmatic approach that when you get up to speeds that are quite moderate even in GA terms, the chance of avoiding a collision visually gets worryingly small. See-and-avoid may work for manoeuvring gliders, but it doesn't work for something doing 200 knots -- and you can scream that pilots "just aren't good enough at lookout" until you're blue in the face but that doesn't change human performance.
Thus the choices seem to be between:
a) the status quo,
b) radically changing the UK airspace system to incorporate more controlled airspace or
c) imposing a see-and-avoid based speed limit in class G and writing off 2/3 of the UK's lower airspace to recreational activities like gliding.
I'm not putting my money on Joe Public writing to his MP to demand option c, are you?
