See? I didn’t consider your post harmful, but I did consider it worthy of a downvote, simply due to how I felt it contributed to the discussion.
And people who don’t feel like I’m contributing meaningfully can downvote my posts. Almost as if that was the point of the button, to give an indicator of how much readers liked or disliked the content.
Negative opinions are every bit as valid as positive ones. Even more so in a culture where criticism is considered “rude” and socially suppressed.