The bottom line is, I really just don't feel comfortable with her going on this trip. He can give me all the logic in the world, and I can give myself all the logic in the world, but that won't overcome my gut instinct that I just don't like it.
I agree with Bug that H's responses were not too bad and something that one would say in a convo. M, can you make an executive decision that you can take full ownership?
Why not tell H, "H, after much thought and hearing your input, I think it's best to keep D at home. This year, she's been over scheduled with way too many trips and skipping one is something that we all can live with. Cool with this?"
Or the second option, "H, after much thought and hearing your input, I think we'll go ahead and let D go on this trip. Cool with this?"
Then H will feel silly for his paranoid text about talking "to your lawyer" behind his back.