As an air traffic controller who has for many years provided a radar control service in class E airspace I can safely say that it is the most awful class of airspace I have ever encountered.
IFR flights are I'm sure blissfully unaware that whilst they are receiving a radar control service, they are not in a known traffic environment.
I can only pass traffic information on known traffic, or unknown traffic that I can actually see on radar. Do you have any idea how poorly many slow moving contacts such as microlights, gliders, and non metallic light aircraft show up on radar? Especially if they are not squawking as is common for this type of aircraft.
IFR aircraft can be legitimately flying at anything up to 250 knots. If youre flying at 90 kts What chance does an average jet airliner have of seeing a tiny aircraft at a potential closing speed of over 5.5 miles per minute? At what range could you even reasonably expect the crew of such an aircraft to even see the conflicting traffic?
Conversely, if the IFR aircraft is rapidly approaching a VFR aircraft in the quadrant between 4 o'clock and 8 o'clock, what is the realistic chance of the VFR aircraft actually sighting the traffic in time to properly assess the relative flight paths and take avoiding action?
These are not far fetched, "what if" conjecture. These are borne out from real world experience and a long struggle to have a well used piece of class E airspace reclassified as class D, which was only forthcoming after a nasty airprox.
I find it astonishing that anyone with the intelligence to fly an aircraft of whatever variety could seriously advocate the increased use of class E airspace. It puts you at risk, and it puts Joe Public in the air and on the ground at risk.
It's not about preventing VFR flights from entering the airspace, it's just about knowing they are there and being able to avoid them accordingly.