The author has a specific opinion about what lawyers are obligated to do; the purpose is to deliver that opinion. The purpose is not just to raise complications. The author is exploring a specific complication — what if a lawyer doesn’t think the client is innocent? — and telling lawyers what they should do.

This captures the author’s opinion. It may not be the exact thing we anticipated, but it’s the only answer that accurately captures at least part of what the author argued.

The author argues that guilt/innocence should be something taken into account. The purpose of the passage isn’t merely to say that this currently isn’t important to many lawyers.

The overall purpose isn’t to discuss issues a lawyer must resolve before accepting a client. Although the author does mention that lawyers shouldn’t accept every client that wants representation, that’s simply a minor point mentioned as part of one of the things a lawyer is obligated to do. The overall purpose relates to the lawyer’s broader obligations, not simply the idea of being selective about one’s clients.

The author never made the point that law strengthens democratic societies. In any case, (E) is much broader than any point the author was focused on arguing. The purpose relates to a lawyer’s obligations. It doesn’t relate to law’s relationship to democratic societies.