"But what if you were "optimistic" and only presented one side of the story, the better to fulfill that all-important goal of persuading people to your cause? Then you'll have a much harder time persuading them away from that idea you sold them originally - you've nailed their feet to the floor, which makes it difficult for them to follow if you yourself take another step forward."

Hmmm... if you don't need people following you, could it help you (from a rationality standpoint) to lie? Suppose that you read about AI technique X. Technique X looks really impressive, but you're still skeptical of it. If you talk about how great technique X looks, people will start to associate you with technique X, and if you try to change your mind about it, they'll demand an explanation. But if you lie (either by omission, or directly if someone asks you about X), you can change your mind about X later on and nobody will call you on it.

NOTE: This does require telling the same lie to everyone; telling different lies to different groups of people is, as noted, too messy.