Seems to me that this is all about some sense that if "I" get round the route using only my own body for energy while "you" use powered assistance at some point on the ride, your achievement should be less than mine. In that sense, I can understand why some may feel that their achievement is devalued by allowing partly powered riders. But who actually loses out, unless an assisted rider supplants an unassisted one in one of the points tables or ACP start rationing places on PBP?
I'm happy to state that I don't like the idea that much but I understand the argument in favour and tend to think that we should give it a year or so and see what the impact has been. If we're over-run by mopeds, then maybe it will be time for a rethink. If there are a couple of riders who might not otherwise have been able to take part fully (which includes the delight of collecting stamps and writing down post collection times in the freezing rain), then surely it's not that much of an issue.
It reminds me a bit of the discussions about having support on long rides like PBP or LEL. Do the groups with a camper van, food laid out for them on arrival and clean kit hanging on the line at each control devalue the achievement of those who ride with a saddlebag and one change of socks? On PBP last time I saw one rider putting his bike in the back of a car at the foot of the Roc. I saw the same guy later on, with his bike, at the Carhaix control. So he "cheated". Do I care? I enjoyed my ride and felt I'd achieved my goal, which was all that mattered to me.