A really great example of why comes to us last week in the pages of Popehat. Read the article -- it's short -- but ignore the predictably asinine comment thread. (Summary: a "men's rights" group sued a women-in-tech company out of existence by abusing a civil rights law.) The core point here is an important one: if you write an over-broad law, people *will* abuse it, probably in ways you find offensive. If this rule provides some kind of reward for abusing it, and no punishment for doing so, you basically guarantee that it will be abused.
Writing good Law is *hard*. Folks always seem to miss this point. You need to be crystal-clear about what you are trying to accomplish, why you are trying to accomplish it, and why you think *this* law will assist that end. You need to write the law as narrowly as you possibly can while achieving those goals, or you are begging for abuse. This applies to any organization, from the SCA to the US: don't write laws without thinking through the consequences very, very freaking carefully, focusing not on what you *want* to have happen, but what will *actually* happen when someone decides to bend your words.
And never, ever invoke the phrase "spirit of the law" -- within a year, nobody will remember what you meant, they'll just go by what you said, interpreting it to suit their ends.
As this example shows, Bad Law can have dire, counterproductive consequences. So try not to be That Legislator.
(NB for the few who might think it: the above has nothing to do with tonight's Carolingian Council meeting -- I actually think we're doing a decent job on the process there. One of my great pet peeves is that Kingdom and Society law is often less well-considered than Baronial, mostly because of Bad Process.)