Strangely enough, the example given by Mr. Option in the previous writeup is roughly the opposite of what happens in a real-world "democratic" example of agenda voting. This is because the informal guidelines for voting on E2 encourage positive voting on well-written, well-thought-out, or just plain brilliantly hilarious writeups, and negative voting on writeups that are a waste of bandwidth according to these criteria. In other words, it doesn't matter so much what you're saying as how you say it; this may be a relatively recent trend in E2, but it has been this way since I've been a member. In some ways it's a good thing: for example, I might agree completely with a writeup saying "Sex is kewl!" but that doesn't mean it has a useful function in the database. On the other hand, many utterly dull, irrelevant or just plain wrongheaded writeups will acquire many upvotes if they are lengthy and well-written.
In the real world of representative democracy and politics, of course, it should not really matter how intelligently or articulately a view or an issue is expressed; the informal guidelines for voting seem to be that what is important is how you, the voter, personally feel about it as it relates to your own life and your own views; the subjective as opposed to the objective. We are encouraged to put more emphasis on the ideas rather than the form of their delivery, a good thing in my opinion; however, in practice, a stunning delivery is what swings an issue, often wrongly.
For democracy to function, as for E2 to function, no guidelines are actually required. I am free to upvote or downvote any writeup I like, for any reason, and the same applies to my exercise of my franchise on matters in the real world: I don't need to justify my vote to anyone, and it doesn't need to make any rational sense. However, for democracy to function well (better than, in this example, no rational decision-making system at all), each person with a vote should be adhering to the very loose guideline of "I will cast my vote in the way that will advantage the largest number of living beings and/or disadvantage the least amount of living beings."
Because we don't usually want to put the time or energy into understanding all the complex nuances of each issue in order to decide for ourselves which way of casting our vote seems to fit the criteria above best, we often take short cuts by voting according to a system or ideology that we have previously decided fits our personal value system; these can include anything from Fundamentalist Christianity to Militant Feminism to Tripped-out Anarchist Mania. This is where "agenda voting" comes in to play - although we are only using the ideology as a decision-making shortcut, one of the practical effects of our voting in this way is to increase the power and further the agenda of the ideology and any groups which are associated with it and control it. To put it another way, if you vote according to Fundamentalist Christian values, you are furthering the agenda of Fundamentalist Christian groups and increasing their power to influence and subvert the democratic process. This can be done at a level higher than the individual voter will ever see - for example, a powerful group can control which decisions are presented to the voting public, and can even control the parameters of allowable debate on issues.
Buckminster Fuller predicted that the Internet would allow true (non-representative) democracy to function for the first time by allowing instant, real-time voting on a large yet practical scale. However, in my opinion the Internet only solves the logistical problems associated with voting; it does not address the problem that each human being has a limited supply of time and energy and critical intelligence for the untangling of complex issues, and therefore has to resort at some stage to the short-cut of an ideology or "agenda". For instance, even though the recent grass-roots Internet democratic movements that have begun to influence politics are a radical step forward, one of the effects they have had is to vastly increase the power of the co-ordinating groups which to some extent control the issues which are debated and voted on, such as moveon.org or the Stop the War coalition.
One way to address this problem might be to restrict democratic systems to small and medium scale districts rather than to require everyone to vote on every issue affecting everyone in an entire country, for example. However, the current political trend is to move to larger and larger democratic areas, a trend which seems to me to be guaranteed to increase agenda voting and the power of the groups whose agendas get voted on. It's just human nature - I can stay interested in politics and exercising my vote for quite a while, but there's a limit, and after I've reached my limit I will make snap decisions based on my held ideologies, even if I do it unconsciously.