How important is it to be consistent?

When formulating laws, or even when simply formulating personal moral standards, an important goal is to be consistent. That is, to apply the rules to all people equally, and to make sure the set of rules doesn’t contain contradictions.

But is consistency always good?

For instance, police recently shut down some children’s lemonade stand because they didn’t have the proper permits to run a business in that town. The police were just being consistent and applying the rules to everyone, but I think any reasonable person can see that this wasn’t really necessary.

The judicial branch places great importance on consistency; in making sure that the outcome of each ruling is consistent with previous similar rulings. But this can go badly, too. For instance, the famous decision of Dred Scott v. Sanford overturned the Missouri Compromise of 1820, which had prohibited slavery in some states, on the grounds that it wasn’t consistent with the Fifth Amendment.

What do you think? Is it always good to be consistent?