Why should their prejudices/biases not be represented? I mean, I personally probably disagree with them, but disagreement is sort of the reason for having voting.
The evidence shows that these uninformed and biased non-voters would take different views on a variety of important issues if they were less biased and more informed. Essentially, the voters represent the 'enlightened' views of the citizenry.
by who, and in what way? Arguably the issue is people are informed, just by misleading information. Whether it be CNN, Fox News, reddit, or the Drudge Deport - they all have their own bias. By asking people be more informed, you're really just adding to their own bias and prejudices with the biases of a larger group of people. People tend to gravitate towards information sources that reaffirm their existing beliefs.
There is a great deal of statistical work that compares what people think and believe. Some of these works try to 'correct' for wealth and education, then measure the gap between the views of certain groups and what their view would be if they were more well educated. Other studies compare what people say in response to survey questions to objective truths, i.e. what are the branches of the US Government, who is the president, who is the chief justice of the supreme court. If you would like more information on how voters and non-voters differ, I suggest that you read some of the work on the subject; I cannot brief you on the subject in a few Hacker News posts, as there is simply too much information.
Citizens (, especially non-voters,) are ill-informed, biased, and lack any incentive to scrutinize their views, as the only change that could come about would be a painful realization that they have been wrong (which nobody wants). If you want to read a very revealing and well-written exposition on this subject, I recommend "The God that Failed" (edited by Crossman).[1]