it's not "minions." Way way way back in the early days of the board we actually discussed what downvotes should mean. Argument 1 was that a vote should only indicate whether or not you thought a comment contributed to the discussion- and not indicate agreement or disagreement. This gave an indicator with a single purpose. Argument 2 was that a vote could also be used to indicate disagreement. This made one indicator mean more than one thing. Some suggested a second vote- in order to keep the indicators clear on what they were reporting.

pg eventually came down on the side of Argument 2, so voting can be either "I disagree" or "you comment is not useful."

I do agree that adding a comment when downvoting is useful to the downvotee, but alas sometimes these come off as mean or supercilious and leave a bad tone in general, spoiling the conversation (or igniting a flame war).