Ideally, I would estimate the negative effects: how many people would later learn I lied and abandon my cause, and how enemies of the cause might use the fact I lied against it, and the reputational harm to my other causes and to my allies.
Not to mention the damage the people who believe your lies might do by acting on them.
Because the official who made the proposal gets to look good for consulting with someone high status. There’s a reason consultants have the reputation they do in the business world and governments have even worse internal incentive problems.