That's a limited and scarce resource. The right approach to pricing a scarce resource is to let the price of it float on the market rather than trying to figure out its component costs and then simply pegging the price to that. Otherwise you're imposing price controls and can end up with shortages.
I agree. However, at this point "we" have to decide what the default rules are, and what is decided now will influence what people think is "fair" two years from now (when, hopefully, bitcoin is in the process of becoming wildly successful).
Also, I've read a couple of popular behavioral economics books (e.g. Predictably Irrational), and I think there might be some irrationality that could make bitcoin more successful. For example, "free" is a magical number. If we can make most bitcoin transactions "free" to the typical user, then that's a huge selling point.
There ARE hidden costs; the reason I want to do the back-of-the-envelope is to figure out how big those hidden costs are now and how big they're likely to get in the future. It isn't rational, but most people would rather have "free transactions", even if they end up paying 10 cents more in electricity costs every month whether or not they actually make any transactions.
(I may move this to the Economics topic depending on where the discussion goes)