Advocating for clients requires honesty. Not surprisingly, the rules of professional conduct speak to this. Those rules, as promulgated by the Supreme Judicial Court in Rule 3.4(A) and (B) of 3:07, the Massachusetts Rules of Professional Conduct, prohibit a lawyer from counseling or assisting a witness to testify falsely. The rationale is that the adversary system, while expecting the evidence to be “marshaled competitively by the contending parties”, expects “fair competition” in the process. See Comment to Rule 3.4. Relevant material is not to be altered, concealed, or destroyed. Falsifying evidence, it is pointed out, is a criminal offense.
Not only is the above required by the law, it is a good tactical way to pursue a case. For example, a client signs interrogatory answers under the pains and penalties of perjury. If the lawyer has “put words in the client’s mouth”, one can only imagine the effect on a case when that is exposed in a deposition or at trial. In so doing, not only would the lawyer run afoul of any ethical requirement, the case would lose its value. Half-truths get exposed in the adversarial process. Believe me, I would rather be the one having the opportunity to expose the half-truth than the converse. The point is to have the moral high-ground is not only correct, it is better tactics.