That analogy conflates two things: The fact that the man doesn't know why the fence is there, and the fact that he doesn't care. If I were the mayor, I'd dismiss his request simply because he hadn't done his research. This is not analogous to tearing down laws or social norms so old and complicated that no one could reasonably be expected to know why they were made in the first place. Maybe laws against homosexuality made sense once upon a time, or maybe they were always a bad idea. But I don't need to know that in order to establish that homosexuality should be allowed and accepted today. If there really were a fence, with no record of who built it or why, that just seemed to be inconveniencing everyone, we really would be justified in tearing it down. Sometimes 2 + 2 is just 4.
Maybe laws against homosexuality made sense once upon a time, or maybe they were always a bad idea. But I don't need to know that in order to establish that homosexuality should be allowed and accepted today
"Need to know" is a strong condition, and I probably agree with you that you don't need to know the relevant history in order to establish that a particular law is a bad idea. But I would also agree that if I'm actually trying to determine whether a law ought to change (rather than trying to justify my pre-existing belief that the law ought to change), trying to understand how the law came to be in the first place seems like a really good place to start.
Or is the convention against discussing politics here silly?
I propose a test. I'm going to try to lay down some rules on voting on comments for the test here (not that I can force anybody to abide by them):
1.) Top-level comments should introduce arguments (or ridicule me and/or this test); responses should be responses to those arguments.
2.) Upvote and downvote based on whether or not you find an argument convincing in the context in which it was raised. This means if it's a good argument against the argument it is responding to, not whether or not there's a good/obvious counterargument to it; if you have a good counterargument, raise it. If it's a convincing argument, and the counterargument is also convincing, upvote both. If both arguments are unconvincing, downvote both.
3.) Try not to downvote particular comments excessively, if they're legitimate lines of argument. A faulty line of argument provides opportunity for rebuttal, and so for our test has value even then; that is, I want some faulty lines of argument here. If you disagree, please downvote me, instead of the faulty comments, because this post is what you want less of, not those comments. This necessarily implies, for balance, that we not excessively upvote comments. I'd suggest fairly arbitrary limits of 3/-3?
Edit: 4.) A single argument per comment would be ideal; as MixedNuts points out here, it's otherwise hard to distinguish between one good and one bad argument, which makes the upvoting/downvoting difficult to evaluate. (My apologies about missing this, folks.)
I'm going to try really hard not to get personally involved, except to lay down a leading comment posing an argument against abortion, a position I don't hold, for the record. The core of the argument isn't disingenuous, and I hold that this argument is true, it just doesn't lead to my opposing abortion. I do not hold the moral axiom by which I extend the basic argument to argue against abortion, however; I'm playing the devil's advocate to try to help me from getting sucked into the argument while providing an initial point of discussion.
Which leads me to the next point: If you see a hole in an argument, even if it's an argument for a perspective you agree with, poke through it. The goal is to see whether we can have a constructive political argument here.
The fact that this is a test, and known to be a test, means this isn't a blind study. Uh, try to act as if you're not being tested?
After it's gone on a little while, if this post hasn't been hopelessly downvoted and ridiculed (and thus the premise and test discarded as undesirable to begin with), we can put up a poll to see whether people found the political debates helpful, not helpful, and so on.