If your honesty means being brutal, issue is you.
> If Hitler had believed that this speech mattered (and he was probably correct that it did not) then he would have just said something different and had the same actions carried out.
Hitler knew his speech mattered and that is literally how he became so powerful? He was literally the speaker of the party. He became party leader only after he established himself as a speaker whose speech matter. Also, what Hitler reiterated in that pre attack speech was what he wanted the troops to do and how he wanted them to act. He was talking about the destruction, because he thought his speech matter and destruction was what he wanted to achieve.
This has nothing to do with honesty being allowed or not - he literally threatens people with execution if they honestly disagree.