I am glad for this article addressing important issue. I have caveats about the Catechism giving the best reason for telling the truth. The foundations of the covenant are not shaken; the one telling lies may be doing himself and others harm, but the covenant we have is not with the Law but with Jesus Christ in spirit and in truth. 
Everyone (excepts psychopaths) has a conscience and has the ability to discern truth from falsehood. 
The question may be posed whether Trump has a personality disorder. But when it came to telling the truth, where was Bernard Law? In the movie SPOTLIGHT he gave a copy of the Catechism to the editor of the Boston Globe after his interview with him.
The Catechism was not enough to inspire honesty. May I suggest that there are better justifications for being honest and forthright with others than this?