Cynicism is and has been in the past many things to many people. I think of today's majority use of cynicism as being a corrective lens, like eyeglasses, required in modern life to see things as they are, rather than as the infinite number of imploring hucksters wish us to see them. A kind of personal spam-deletion mechanism.

So in that sense, I guess, you could indeed call it a defense mechanism, but then you risk getting involved in all the arguments and disagreements that have cropped up over the other, natural defense mechanisms. I'd prefer, myself, just to leave it as a conscious personal option to use when you're tired of having been suckered once again by those seeking to take advantage of you.

Anyone who denies the necessity of cynicism in today's world is obviously either dissociating like mad or a tool of the other side, the flim-flam people if you will, whether consciously or unconsciously. Fifty years ago, "Little Mary Sunshine" was funny. Today it's either a tragedy or a horror movie, take your pick.