Another major point was the effectivness of a fraction of the maximum harm possible inflicted over a long period of time. It would be more effective in a bargaining process to only kill one hostage/ kill 100 POWs/ nuke one city rather than threatening maximum harm immediatly after your action.

First of all, good analysis of the meaning of honesty! However, I see several problems with your application of this to the real world.

I think in most cases phrasing unintelligible for one group would not lead to them adopting any beliefs whatsoever. People also are not blank slates, just waiting for anyone to give their opinion on something, rather they have established worldviews and networks of beliefs, so your arguments might nudge somone already going in a particular direction, but will not make anyone believe something completly different. Also, I think you are overestimating the number of ways in which a statement can be interepted (I can not see how "The bill will increase the national debt by 12%." could be interpted in maéaningfully differnt ways. But feel free to give me counterexamples.)