I'm not saying it's unsafe to cross VFR, and I'm sorry if you think that was my point.
My opinion is that it's simpler to cross IFR, as one of the side effects is to shift area avoidance from pilot to ATC.
As an example, look at a VFR route from Geneva to London. You will see many restricted areas over France, plus the Dijon, Reims, Paris and Lille terminal areas. Crossing them VFR requires many co-ordinations, and increases pilot's workload. It's by far not impossible, but it's complex.
Flying it IFR, the route is DJL - REM - ABB - DET, and all controllers along the route know you in advance and vector your around potential restricted areas.
Once again, I don't see anything wrong in VFR, I simply have to say that IFR makes the en-route navigation much easier.