A few ideas I've recently read (including this one) have sparked the following line of reasoning; and I'm curious what the general LW opinion on the idea chain might be.
If two neighbouring societies are unequally skilled at the art of war, then the worse one will soon come to resemble the better; either by being taken over outright, or out competed and displaced, or adopting their neighbour's attributes out of sheer self-defense. Thus, by knowing what is required to win a fight, and what it takes to support that requirement, you can make a reasonable guess about the shapes of the societies.
Part of the Agricultural Revolution, the shift from bands of hunter-gatherers to fixed settlements, was the development of formal standing armies. It took heavy taxes to support them, and a centralized bureaucracy to manage them, resulting in the Classical Empires: Babylon, Rome, and the Aztecs had a great deal in common. Later, improved metallurgy and arms resulted in heavily-armoured knights who could hold off any number of unskilled peasants... and the manors required to support them resulted in the feudal system. Later, around the Renaissance, crossbows, pikes, and guns unseated the knight from military dominance; and the system that best supported that sort of force turned out to be the republic. Later, the Industrial Revolution kicked this sort of thing into high gear, with new military paradigms arising every few decades: ironclads, tanks, planes, nukes. Supporting all of these required the economy to be cranked up to the maximum degree possible to make all that stuff, and scientific research as well to figure out the next trick. As it happens, the form of society that seems to work best at that is something resembling a liberal democracy. (At least, more than it resembles a military junta.)
Thus, if you want to predict what future societies will look like, a viable approach could be to examine this present-day societies which do the most and best science, and figuring out what lets them do that. For example - having enough freedom of expression to allow unpopular ideas to be evaluated on their merits.
This also begs the question, if that's what things will look like later, why don't they look that way already? One strong possibility for the answer: those powerful people who don't care about any of the above, but only about their own immediate short-term gain, regardless of what damage they do to the society surrounding them. Such entrenched interests act as a drag, preventing both the economy and scientific research from proceeding at maximum speed... And, thus, whether they are willing to admit it or not, their behaviour is sabotaging their society's odds of success in its next war; thus increasing the odds that the very social systems they exploited to enrich themselves will be replaced by force (instead of by gradual evolution as new social forms are demonstrated to work better).
Thus: as it has been mathematically proven that a copyright period of more than 15 years causes harm to the overall economy (while a small group reaps obscene profits)*, anyone who tries extending copyright beyond that length is traitorously allowing foreign powers to gain a military advantage, and risking the takeover of their countrymen's government by alien interests, for nothing more than their own personal aggrandizement.
The only rational conclusion: You must work to shorten copyright... to protect your children.
One of the best ways I know of to work towards a social change is to live that change yourself, accepting the negatives even though the positives don't exist yet. In this case - the above reasoning may lead me to decide to declare that, to the best of my ability, I will try not to pursue any copyright claims on any of my work that has been published more than 15 years previously (while still accepting any remuneration from anyone who wishes to thank me for such work anyway). While for me this is a symbolic gesture at best, as best as my back-of-the-envelope math can figure out, for people who actually have money-making copyright claims, the odds that their own gesture will have a positive effect scales roughly evenly with the potential profit they stand to lose.
I'm seeking out at least a couple of different perspectives, to get some further feedback on how erroneous my reasoning might be.
*: Source: http://www.rufuspollock.org/economics/papers/optimal_copyright.pdf , where, even when granting the longer-copyright side the benefit of the doubt on every questionable assumption, the maximum beneficial length of copyright was still found to be no more than 14 years.)