After reading the responses so far, I would gather that there are two questions involved.
1. Can a practicing lawyer be completely honest?
2. Can the arguing of the black and white of law be a honest profession?
IMHO, A "good" lawyer's job is to get what his client needs, any legal means available. Legal means can, and does, include belittling, not telling the whole truth, digging up the opponent's past, hiding your client's past, etc. etc. And by the way, the Insight book's definition does fit with the legal perspective of a lie.
As for arguing the justness of a legal stand point? A noble profession - but that doesn't make lawyers noble. Ask anyone who has gone through a divorce - almost, if not all, will want a "good" lawyer who will protect your interests. Someone else can pay the noble lawyer.
Can they not lie? Of course. There is a spectrum of shades of truth. (No pun intended.)