Propaganda, a word derived from New Latin in the seventeenth century, did not originally carry the negative associations with which we identify it today. Yet with propaganda there has always been an intent to "propagate," or, in more religious terms, to "proselytize"—that is, convert, persuade, and sometimes indoctrinate.
Propaganda is generally a means of transmitting the ideas and belief systems of political, religious, or other groups in an effort to affect the opinions of the wider public and to garner more support, as well as to combat counter-opposing forms of propaganda. But in the course of the twentieth century, when governments began utilizing their own mass propaganda to support their ideological agendas, the nature of propaganda as indoctrination became much more common. The state throughout history has always propagated ideology among its subjects, but with the development of mass communications in the nineteenth and twentieth centuries, propaganda as a systematic tool became common practice in governments' political strategy, in order to influence their and (in the case of war) other countries' populations.
In this sense, propaganda is essentially undemocratic, because it overvalues the government's position while undermining any others. But as previously stated, propaganda is merely a form of communicating ideas, whether or not those ideas contain some kind of agenda, and whether their intent is to suppress or liberate the ideas of the democratic body. So, any social group can propagate their ideas, without necessarily utilizing power to control the beliefs of the people at large.