is there actually evidence that (a) most PPLs can/do fly VFR on top, and (b) they don't have accidents whilst doing so. Apart from anything else, my experience as a researcher is that outside of the UK, US, Germany and Australia, most countries safety statistics are so poorly compiled that you can prove just about anything, or nothing. And again, I'm aware that ICAO standard permits VFR on top, but how many countries actually permit that?
All US PPLs can fly VFR on top, and it's perfectly normal practice in the US. I may be wrong, but as I understand it, the JAR-FCL PPL allows VFR on top, it's a UK restriction. I am not sure if any other JAA countries also implemented this restriction, I don't think many did, if any. I imagine plenty of French PPLs fly VFR on top on their long Class E airways.
Hence my point about the majority of the world's PPLs. You're the one who made the point that "I see no argument in favour of permitting" something that is a normal part of the PPL privileges outside the UK, so you show me the evidence supporting what I find an extraordinary claim. The FAA have hundreds of thousands of PPLs without IRs. They publish papers and educational material on all sorts of flight training and risk management topics. Show me one advising against VFR on top, or highlighting the risks thereof. The NTSB accident database is searchable and has a vast volume of data. Do your research thing and show me any evidence suggesting VFR on top is dangerous.
brgds
421C