As for the history of the option: it has been around since the inception of the network, and a major cornerstone of the SE philosophy. In fact, I believe there is an old blog post where Jeff Atwood announces that he made downvoting of questions cheaper in rep for the downvoter, since the feature is used too seldom.
The reasoning behind it: it is done in order to make it easier to distinguish between good and bad questions. The most direct positive effect is on the "silent readers", which is the millions of people who read sites on the network without ever making a post or a comment. (That's the demographic whose interests are given preference in SE network design). Sorting by score is an important way for them to get quicker to more informative pages. Also, negative scores are a very good information source that enables not only sorting, but also automated cleanup*.
As for the more active community members, they also enjoy the advantages provided to the readers (sorting, less garbage on the front page, etc.), but are also given an important tool to actively communicate their opinion on what kind of question they don't want to see. This is even more important than upvotes, especially when one notices how rarely a downvote is given.
And lastly, for the asker, it is a very strong incentive to discourage the asking of similar questions. While every site has a handful of people who persistently ask questions which get regular downvotes, most people are sensitive to negative feedback and react to it by either learning more about the rules of the site, or by refraining from posting.
And yes, I am aware that some people find the principle unfriendly. This is seen as an unavoidable side effect of the network's main goal, which is to provide strongly curated content. We are an environment which provides content very selectively, and where there is selection, there is also rejection. The founders saw this as entirely appropriate for a professional, content-oriented resource which actively deemphasizes the social nature of other formats such as discussion forums.
* I am aware of the irony of this very question having fallen victim to unwanted automated cleanup. Sadly, it does have side effects.