Science literacy does not have a unique definition. Depending on what your ideas about science are, the meaning of science literacy will change. But being scientifically literate, is usually taken as a sign of being informed, being rational in decisions. Here is what the great science and science-fiction writer Issac Asimov had to say about its importance.

A public that does not understand how science works can, all too easily, fall prey to those ignoramuses … who make fun of what they do not understand, or
to the sloganeers who proclaim scientists to be the mercenary warriors of today, and the tools of the military. The difference … between … understanding and not understanding . . . is also the difference between respect and admiration on the one side, and hate and fear on the other.
– Isaac Asimov