If everyone’s in agreement, there’s nothing left to discuss. If we both thought “Disagree” shouldn’t exist, we wouldn’t need to have this conversation.
This is only true in the very narrow context of a single post; in the context of the whole conversation, including both buttons is biased towards disagreement. Consider again the scenario of a feature request / bug report. Someone had to put in the effort of explaining
why they think it’s valuable. Why should someone who disagrees not have to do the same?
…which is a bad thing. Emphasizing community sentiment encourages groupthink and is harmful to thoughtful and civilized discussion. Votes in either direction bias people towards/against the post, regardless of its merit; downvotes in particular can be discouraging and drive away unpopular voices, creating an echo chamber and a false sense of consensus.
So, why include a "like" reaction at all?
Showing support for a post does have some value. For example, receiving a bunch of
+1's on a feature suggestion or bug report suggests that we should prioritize it. In contrast,
-1's don’t mean much without an argument behind them. It’s hard to address concerns if you don’t know what they are.
There’s also a couple things minimizing the negative impact, making it a better trade-off:
- Reactions don’t affect post visibility. (they might affect the “Top” sorting, but that’s not the default)
- They’re shown at the bottom of the post, so people don’t see them until after reading.
- Having only one reaction weakens the effect, since each person can only project half the influence.
- “Like” is the less harmful reactions, to whatever extent promoting popular opinions is less harmful than silencing minority opinions.
I consider reactions to be a quick way for people to give feedback on a post — particularly the type of short feedback that would otherwise clutter the thread (some people there have since taken my advice; that issue used to be even longer).
Github (ab)uses and for pseudo-polling, but that’s because they don’t have proper polls. We do.