I will not reiterate the many specific criticisms of the memos already made by those with far more expertise than I. A very large number of international law experts see the memos as deeply flawed, as did the Office of Legal Counsel itself.
The job of an ethics lawyer and indeed any lawyer who is a generalist is to spot issues and to identify both legal and nonlegal risks to the client. Here the memos appeared one-sided on their face and it was obvious that the subject matter could expose the United States to widespread condemnation. Whether or not the advice is technically correct, a client is entitled to be told when there are arguments on the other side and when there are risks in proceeding as planned. None of that happened here. I cannot point to specific passages of the memos to illustrate what wasn’t there.
It could be argued that the client wanted the advice given. This is common in corporate representations where officers or directors ask for an opinion of counsel stating that they may do something they shouldn’t do. Rarely is the opinion given because if it is, and the matter blows up, the corporation, perhaps under new management, can turn around and hit the lawyer with a malpractice suit. Not true in government.