+1s could mean

-Someone agrees with you

-Someone likes you

-Someone is happy or having a good day

-Someone is repaying a favor or maintaining a friendship.

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.

> are reluctant to -1 as it signifies conflict

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 you're saying at a glance looks non-insane

That's like 90% of the PR's I look at.

If you get a -1 from somebody whose opinion you value, you can always ask what's up.