That, and for certain kinds of fences, if there is an obvious benefit to taking one down, it's better to just take it down and see what breaks, then maybe replace it if it wasn't worth it, than to try and figure out what the fence is for without the ability to experiment.

Good point. Some properties of a system are accidental. ---------------------------------------- "We don't know why this wall is here, but we know that it is made of gray stone. We don't know why its builders selected gray stone. Therefore, we must never allow its color to be changed. When it needs repair we must make sure to use gray stone." "But gray stone is now rare in our country and must be imported at great expense from Dubiously Allied Country. Can't we use local tan stone that is cheap?" "Maybe gray stone suppresses zombie hordes from rising from the ground around the wall. We don't know, so we must not change it!" "Maybe they just used gray stone because it used to be cheap, but the local supplies are now depleted. We should use cheap stone, as the builders did, not gray stone, which was an accidental property and not a deliberate design." "Are you calling yourself an expert on stone economics and on zombie hordes, too!?" "No, I'd just like to keep the wall up without spending 80% of our defense budget on importing stone from Dubiously Allied Country. I'm worried they're using all the money we send them to build scary battleships." "The builders cared not for scary battleships! They cared for gray stone!" "But it's too expensive!" "But zombies!" "Superstition!" "Irresponsible radicalism!" "Aaargh ... just because we don't have the builders here to answer every question about their design doesn't mean that we can't draw our own inferences and decide when to change things that don't make sense any more." "Are you suggesting that the national defense can be designed by human reason alone, without the received wisdom of tradition? That sort of thinking led to the Reign of Terror!"