The difference is when you +1, you're publically expressing agreement with what they wrote. If someone you like writes something you don't agree with, you wouldn't +1 them. If you're having a good day, you still wouldn't blindly dish out +1's because if you +1 a controversial comment, it could hurt your reputation.
Negation is different because it's entirely ambiguous. You can dish them out freely and retroactively rationalize your intention. -1's are way more susceptible to knee-jerk emotional reactions than +1's.
A relevant example. Think of the political candidate you like the most. If someone you really like asks you to +1 a persuasive argument about their competitor, would you? On the other hand, if they asked you to -1 someone, you probably would. Even if you knew very little about them.
My experience of open source projects is that people dish out +1's freely and are reluctant to -1 as it signifies conflict. +1 is arguably the more ambiguous for that reason as it can mean "I didn't read the issue but I like you and what you're saying at a glance looks non-insane" or "meh" or "I love it". You're really underestimating the ammount of politics that can factor into these things, people will +1 something that they 90% disagree with because of who's saying it, don't kid yourself otherwise.
Nobody really cares if you +1 something crazy, maybe you were just feeling agreeable that day, or you misunderstood the comment. But if you -1 sensible things you're going to get a bad reputation pretty quickly.
That's because people don't tend to write "-1", but rather disagree with a comment explaining why. GitHub is full of disagreement. We'd be in a much worse place if that was all expressed through downvotes instead of comments (unless of course, an issue is explicitly opting in to a vote).
> people will +1 something that they 90% disagree with because of who's saying it, don't kid yourself otherwise.
Ok yeah, you're right about the politics. Bad example. But in open source, I've seen much more comment-based pushback regardless of author.
What about a comment? Once someone elaborates why they disagree, others can trivially +1 it to show support of a specific disagreement.
On the other hand, you can disagree with both the original comment and someone's disagreement, prompting an additional "disagreement" reply.
Note that -1's don't carry as much information as you'd think. It could mean any one of these:
- Someone disagrees with you
- Someone doesn't like you
- Someone is angry or having a bad day
- Someone is retaliating or holding a grudge
Without any rationale, there's absolutely no way to tell the difference between a useful disagreement and juvenile aggression.