In the simplest terms, propaganda is an attempt to convince someone of something through means other than presenting theses and defending them with arguments and evidence. In my opinion, this includes about 95 percent of the content of television, which is why I don't have one anymore. A TV show is not a communication of ideas, and it is not education. At its absolute best, it is entertainment. When that entertainment is used to mask a subtext, utterly regardless of what that subtext entails, then it is nothing but base propaganda. Propaganda (from the original Latin phrase "Propagation of the faith" that referred to the Pope's infallible pronouncements in the middle ages) is what authorities have long used to quell dissent and keep what Walter Lippmann calls "the bewildered herd" in line. It also necessarily presupposes that the people creating the propaganda hold the intended audience in utter contempt.
People are not blank slates and passive recipients of information. To educate is literally to draw out (Latin e + ducare) - that is, to allow people to flourish and become what they can be by drawing out their innate abilities and cultivating the most noble human qualities. Propaganda is the inverse of this - it attempts to mold people into accepting externally imposed constraints and limitations. Embedded in the propaganda effort is the assumption that people they are incapable of forming their own opinions and hence cannot be trusted to independently act in a responsible manner.
The means of propaganda are to appeal to fear, greed, self-doubt, and jingoism in order to reinforce the worst human qualities. People under a system of propaganda come to believe the assumptions implicit in this means of control, and to hold themselves in the same contempt in which authorities hold them. People abrogate responsibility for their own actions and allow themselves to be ruled. You can see this happening dramatically in the wake of 9-11, as people rush to accept liberty-infringing security measures that would normally outrage most citizens.
To engage in propaganda is to press for a kind of benevolent despotism. Enlightened despotism, fascism, dictatorship (a dictator is literally 'one who speaks'), whatever its stated values, is always and everywhere crushing of the kind of human freedoms (the opportunity to act coupled with an ethical imperative to act responsibly) that would make a sustainable culture possible.
But after all it is the leaders of the country who determine the policy, and it is always a simple matter to drag the people along, whether it is a democracy, or a fascist dictatorship, or a parliament, or a communist dictatorship...Voice or no voice, the people can always be brought to the bidding of the leaders. That is easy. All you have to do is to tell them they are being attacked, and denounce the pacifists for lack of patriotism and exposing the country to danger. It works the same in any country. (Hermann Goering, Nazi leader, during the Nuremberg Trials)