Thumbs Down Button

This is purely based on curiosity, why is there a thumbs up button but not a thumbs down?  I'm not necessarily advocating to add this feature, I am just curious.  Thoughts?

There have been several discussions of this in the past and IIRC Nick is fully against it. If you search for “thumbs down button” on the site you’ll find a lot of forum posts about it.  

Same reason facebook doesn't have it (or dislike button in this case)

Now where is the thumbs down button when you need it? ;)