Yes, nursing a baby is not porn and is a natural part of life. After all, the mammary glands were designed primarily for that purpose and not simply for entertaining the opposite sex.
Defecation, urination, flatulence, belching, and having sexual intercourse are also natural parts of life, but civilized societies have learned to instill some modesty when it comes to those innate actions.
Exposing or posting a picture in public of one's nipple, regardless if a baby or adult mouth is near it, is a repugnant act to anyone with any sense of gentility. When breasts are presented with an in-your-face attitude at a social gathering (cyber or live), it is pornographic and is best left to the privacy of the bedroom.
There is something beautiful about a mother nursing a newborn, but it is most seraphic when it is done discretely, quietly, and intimately, and not made a public spectacle on a social networking site.