what does the quote: " My daddy always said in the land of the blind, the one eyed man is king" mean

Well, if everybody else can't see so even having one eye makes you powerful. The drug dealer has both his eyes cut out. The metaphor ( I think) is that if you have the insight that everyone else is blind to , one has ultimate power.

Also the idea that in a society where everyone else has two eyes, the person who has only one is looked down on, or imperfect. In a society where no one has eyes (is blind) the person with the one eye is superior, at the top. it's all a matter of perspective.

When one is blind, one does not know when one is being watched.  And in the land of the blind, the man with one eye can keep an eye on you.  ;)  If u want to know more about "watchers" and why they are considered as "kings", here's a link: http://www.bibliotecapleyades.net/vida_alien/alien_watchers07.htm

I'm pretty sure it refers to the fact that in the movie the future crimes police, and the people who run it, have developed the ability to see things that noone else can (the future), this gives them a an advantage over everyone else in society, which allows them to in effect rule over how people behave, ergo "in the land of the blind (society) the one eye'd man (the future crimes police) are king."