Most people are indignant at the suggestion that they are not reliable authorities about their real wants. Such self-knowledge, however, is not the easiest kind of knowledge to acquire. Indeed, acquiring it often requires hard and even potentially risky work. To avoid such effort, people unconsciously convince themselves that they want what society says they should want.
So the passage is saying that Most people get angry/upset when someone tells them they don't know what they want. It is not easy to figure out what people truly want, for that one has to see things as things are. This knowledge of objectively seeing what people want is earned by hard and potentially risky work. So people unconsciously convince themselves that they want what society wants them to want. Why would people unconsciously convince themselves to want society's idea of themselves. Because it is not easy to see things as they are and thus most people take the easy way out unconsciously.
The main point of the argument is that
(A) acquiring self-knowledge can be risky - Haha, not really. Passage says the work may be risky not the knowledge itself.
(B) knowledge of what one really wants is not as desirable as it is usually thought to be - It is very desirable to know yourself, As Aristotle puts it - to ti ên einai
(C) people cannot really want what they should want - No, this is opposite, people can want what they truly want.
(D) people usually avoid making difficult decisions - Maybe true, but this is main point question and answer must capture jest of whole paragraph. People sometimes can take the difficult route and learn to want what they truly want.
(E) people are not necessarily reliable authorities about what they really want- Yes, this must be main point of the paragraph. People are not necessarily reliable authority on themselves. This captures the central idea of the passage. E is the answer.