Being willing to argue one's point is not a bad thing. The guy that placidly goes with what you say likely didn't really understand what you were telling him. I get nervous when I get too quick agreement. Sometimes that is the prelude to blowing me off or totally misinterpreting my instructions.
The arguer might not really understand you but in the exchange, there is going to be a real hashing out of the matter at hand. At least you know he was thinking about the subject at hand.
Wes
-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller