The political problem is that some people would be charged more; regression to the mean suggests that those people would be the ones who currently pay the least. The people who pay the least are the people who use the least power.
In a proper cost-sharing setup, dividing the fixed cost of maintaining each portion of the grid among the people served by that portion of the grid, pricing would be fiendishly complicated and appear unfair: Consider ten rural houses roughly in a line sharing a single branch line from the distribution station: each of these houses would be charged equally for their use of the larger distribution network, but the first house would be charged with 1/10 the cost of maintaining the first segment of their shared circuit, the second house would be charged that plus 1/9 the cost of the second segment, and so forth.
Or is it: If someone builds an 11th house at the end of that line, and the added load requires that the first segment be upgraded (to a line with higher maintenance costs) to handle the additional load, how is that cost fairly distributed? (What if the 11th house is added in the middle of the line?)
A $X+$y/kWh system makes more sense, but there is no system which is perfectly fair and appears to be fair to most people.
The political problem is that some people would be charged more; regression to the mean suggests that those people would be the ones who currently pay the least. The people who pay the least are the people who use the least power.
Everything you say is true, but your implied argument is flawed (you are implicitly making an "all A are B, all C are B, therefore all A are C" argument). If we had a fixed fee, and were discussing the possibility of eliminating it, your argument would apply just as well.
Example nicked from this online Berkeley lecture.
Monopolies are bad (morality and economics agree here).
Firms that pollute are bad (morality and economics agree here).
What about monopolies that pollute?
What about strong monopolies that pollute and receive government subsidies?
Well...
Pollution, and other negative externalities, cause firms to produce too much of their product. That's because they don't pay the full cost of the product, including the impact of pollution.
The equilibrium behaviour for monopolies is to produce too little of their product, to keep prices and profits high.
So a monopoly that pollutes is subject to two opposite tendencies: the unpriced-pollution tendency to produce too much, and the monopolistic tendency to produce too little. If the effects are of comparable magnitude, then the monopoly might be much closer to social optimum than a free market would be (the social optimum, incidentally, will generally involve some pollution: we need to accept some pollution in the production of fertiliser, for instance, in order to have enough food to stop people starving).
In fact, if the monopolistic effect is too strong, then the firm may under-produce, even taken the pollution effect into account. In that case, we can approach closer to the social optimum by... subsidising the polluting monopoly to produce more!!
And that, my friends, is why economics is not a morality tale.