I note that the body of your comment implicitly agrees with me that providing evidence is a good thing :)

The character of a community is formed by what it does more than what it says it does.

I would tend to agree that it usually does benefit the discussion to say why one disagrees instead of a simple drive-by downvote, but when folks have already agreed to disagree or are in the process of reaching such agreement, more rabble-rousing inclined folks tend to jump into the fraying thread to sow discord, so I understand why it’s not in the guidelines that we must specify why we downvote or flag instead of just doing so.

More from dang on this topic here:

https://news.ycombinator.com/item?id=12334384

The whole comment is worth a read, so here’s just a taste:

> Our goal is to optimize HN for intellectual curiosity, which requires a higher signal/noise ratio. Downvotes dampen low-value comments. I know downvotes do bad things too, but that's the good thing they do, and it's big. Taking that away and/or increasing the noise with a flood of people disagreeing about their disagreements would not be an optimization.