This is a Progressive Blogger Union entry.
The basic definition of propaganda is simply information for the purpose of advocacy. Neutral in the dictionaries, in common use it has picked up the connotation of deceptive information, or dishonest advocacy, and as such is often a word used to describe information merely put out by people advocating a position with which one disagrees. When two sides have equal voice in a debate, the addition of spin isn't particularly significant, other than the morally corrosive effect of deciding to try to deliberately deceive an audience. When a government or corporation is involved, however, it is a much more serious matter; the sheer imbalance of power and communicative reach require that societies attempt to constrain deception, lest the entire society be reduced to making critical decisions based almost entirely on falsehoods.
