When you read the news, don’t see the article you are reading in isolation. Try to see it in the context that produced it to draw understanding of our world from it.

It is the simpliest answer. Totally correct, but I hoped for more, when clicking title.

1. It is not enough to read news media to get the context, allowing to judge reliability of news. I'd propose to read some books, to take a bigger picture, to grasp historical process which we are part of. To grasp some idea of metaphysics of human history. I couldn't explain what it is, because it is too complex and difficult to explain, it seems like my neural networks have learnt some generalizations from a very wide context, but how it often happens with neural networks no one could explain how they work. It gives ideas of what is possible and what is not, what is probable and what isn't.
2. We could move on level lower and search article for signs of bias. If we knew bias, we could undo it. The good example of the most blatant signs s the journalistic art of Rita Skeeter in Rowling's Potter. Speaking of which Rowling failed to show how to work with such a journalism, her heroes either ignored Rita or (like Harry in the last book) felt pain from inability to separate lies from facts. It is possible to extract facts from Skeeter's articles, to throw away everything else, and to see a picture which is as real as it is possible. But Potter dived into a reality pictured by Skeeter and then painfully tried to resurface. It was a mistake from the beginning (though understandable, Potter was 17 at that moment, and one of his hiddens powers to fight Voldemort was his emotionality).
3. To measure bias we could evaluate not just the single article, but a lot of articles of the author of the article, or from the same publisher. To do it I systematically read news from several resources. Even when I cannot find nothing interesting for me, I pick some article at random and read it. This way you learn a style, you learn a narrative, you learn to predict what this media would write for any occasion, and your mispredictions will be very informative.
4. Read different sources. Truly different. If you read NYT, add Fox News to your reading list, but do not stop there, add something completely different, something outside of the system you watching. It is very hard to understand a system being a part of it. Some believe that it is even impossible. Though it is a deep philosophy.
5. Read a textbook on experimental psychology. I believe no science know about experiments as much as psychology. Physicists do not know as much, because they deal with simple systems without brains. They are not forced sometimes to abandon experiment and use pseudo-experimental plans, or other reseach plans. They need not to invent a new physics each few years, so they know how to exist with a ready-made theory, but they know a little how to deal with reality where all theories were failed. Sociologists deal with too complex phenomena to be successful, and they mostly stuck with correlational research plans (so no reasoning about causality). Psychology is in the between, it could struggle with inability to devise an experimental plan, and at the same time it have a chance to devise it and to test it on real subjects. Textbook on experimental psychology could give you the theory and some practice to learn how to evaluate a validity of a research. It helps a lot even if I read an anonymous comment in internet, not just when I'm reading a psychological paper.

("Snow is white" is true) if and only (snow is white)

"if and only IF", isnt it?

the notion of truth is quite different

Broken link to http://yudkowsky.net/bayes/truth.html

Not only the culture of disagreement takes place. When I see "+1", I think what a mind processes do that: commenter needs some attention but have nothing to say? And so when I want to post "+1", I do not do that, for someone didn't think the same about me. Usually I'm trying to make some complement to original post, or little correction to it with clear approval of the rest. Something not important and, at the same time, not just "+1".

There is a way to solve this problem, but it dangerous. Rationalist can watch discussion closely and not only clever thoughts, but the common effect that discussion have on other watchers, and make some activity every time when discussion have wrong effect. But doing this rationalist makes political discussion from rational.

The only way is to remember the purpose for communication takes place. Not every communications is discussion. And this is the most rational way: rationalist every his move should do knowing the purpose for this move. When we speak about cooperating rationalists, we should also remember that there are common goals and individual goals, and rationalist should weigh both and every time pick the most important at this moment.

And in context of donations: what the reason for rationalist to publish his reasons to not donate? Guilt and attempt to justify himself? Or maybe attempt to draw attention: "now look guys how clever my thoughts"? All the reasons I can imagine is individual goals, that this "rationalist" is considering more important than common goals of community. So either this "rationalist" is enemy of community, or he is just stupid (the same thing, generally).