A great debate, this, and a lot of people are right IMHO.
The "IR traditionalists" will never admit just how much less pilot expertise is required to fly IFR safely, relative to the amount of crap one has to learn to get the IR. And I suspect many of them don't actually know - they are instructors/examiners who have never flown IFR for real, or not in anything remotely recent.
MM-Flynn's points are probably very right, but lots of things are self limiting as regards risk. The IMCR is self limiting due the factors he lists, but the IR (as it would be used by private pilots) is also self limiting, due to
- most GA "wreckage" can't reach the levels at which Eurocontrol routings are reasonably easy to develop (basically, FL100 plus)
- most GA "wreckage" can't reach the levels at which a non-deiced plane is going to be viable enroute i.e. flying VMC above typical N European stratus cloud tops (basically, FL120-FL160), so the risk of (to quote the often expressed fear of ATCOs) the airways clogging up with Cessna 150s is practically zero
- most Eurocontrol routings need oxygen, but a lot of pilots won't use the stuff
- many/most (?) owners of genuinely IFR capable planes already have an IR so there would not be any great pent-up demand
- most IFR GA would be flying in the great empty void FL100-FL200 in which there is almost no enroute traffic, and Eurocontrol routings don't compute through terminal areas...
- private GA rarely flies proper-IFR in really poor weather. In fact, IMCR pilots fly in worse weather; one can fly "VFR" in IMC at 2400ft in a typical OVC007 warm front scenario, but one would not go properly IFR in that because the route will be FL100 plus, but the 0C level will be say FL060 (like today; I've just been up there), and the tops will be ~ FL250, so without proper de-ice this is a no-go because the option of a descent to warm air is not there (short of an emergency declaration, and in much of Europe the obstacle clearance will be an issue) and a climb to VMC will mean transiting through 8000ft of icing conditions and anyway nothing short of a PA46 is going to make it there... Generally, I have flown in much worse conditions on the IMCR than I have flown on the IR.
- the vast majority of long distance touring is done in reasonable weather, because who wants to go somewhere when it is pi55ing down with rain?
However, how relevant any of all this is, I don't know. Rationalising is a wsate of time. The actual obstacles are wholly political...