Could we built Angels without Demons?

I recently read a novel by Dan Brown (author of Da Vinci Code) named Angels and Demons... I don't know how to interpret the title of the thriller... But it seems that the author has been extremely philosophical in naming his murder mystery... In the novel where murders occurs in the Vatican under the banner of Illuminati a lost brotherhood centuries ago there were mention of angels every where but where is the demon and why demon was what my inquisitive nature asked me... There was a war between science and religion.... was the demon a representative of the demonic nature of human.... It can always be.. But a few lines there in the novel made me philosophical in this world everything came in opposite from religion to science everything... If I am a bit religious I have godliness as because i have exactly the opposite satanic... If I am a social scientist I believe in equality as i have inequality I have rich as I have poor I have democracy as I have dictatorship... Isnt it strange that everything in this world has opposite in science I have man woman ... and even in physics I have positive charge negative charge.... the language of science in mathematics has positive negative.... The recent experiment to unveil the secrets of dark energy has matter and anti mater.... And what is more strange that without any of these we cannot understand the other we cannot have felt happiness if we have not gone through sorrow and vice versa... We could not define a man completely without the conception of woman and so on... Actually the whole of this world is made in pairs to keep balance.... when we say that this has no side effects we are wrong we have simply known one side of the picture.... The only line that I can think from the book that perhaps a single subject like science is too young to understand it... Perhaps the only way to explain these phenomenon is a bit philosophically..