Disseminating defamatory material is legal __provided you did your due diligence__. Whether taking the journalist at face value is due diligence, I don't know.
This is a common dilemma in social media. Does "liking" a post mean you agree with it? Does "angry face" mean you disagree? What about "laughing face", "shocked face"? It is dangerous to read legal responsibilities into an action which is probably meaningless.
Is disseminating a link to defamatory material illegal? Should it be? In this case, it was a link, not the content itself, which was shared. If Facebook added an excerpt, I would think liability falls to Facebook.
Also note that I'm more interested in what is moral/just, not legal according to any specific system, since this is a discussion about laws which vary across nations. The American/English system isn't necessarily ideal.
Sounds great in theory. In practice I, like most people, only do the due diligence on stories I disagree with. When a story confirms my biases, I accept it at face value. I don't even realise I'm doing it. It's not a conscious decision.
I recently found a subreddit where people had shared an article from a newspaper with a decent reputation. The story strongly implied that the government had engaged in crony capitalism. 96% upvoted, all the comments castigating the government. Normally I would have agreed and moved on. I certainly wouldn't have spent time fact checking an article that I agreed with. Except it was about something I knew a bit about (solar energy). The article was wrong and misleading. Perhaps even "fake", considering how many people had been misled.
When I tried to correct the record on the same subreddit, there was huge pushback. People nitpicked my fact check to death. It got a small fraction of the upvotes and comments the original fake/misleading article did.
None of those people did the due diligence, like you want them to. All of them took a journalist working for a reputable newspaper at face value. Should they all go to jail now for upvoting and commenting?
Defamation is not a criminal offense. Nobody goes to jail for defamation. You can be sued for damages from defamation in civil court.
I never said what I wanted, or gave any opinion. I'm just adding a bit of color to the conversation by stating relevant facts. The accusatory tone is not very conducive to interesting discussion.
More to your question, I highly doubt upvoting a reddit post counts as dissemination / publishing. The comments people wrote could themselves be defamatory, but I also doubt a reddit comment will cause demonstrable damages to a person's reputation. There has to be damages for you be sued, otherwise there is no reason for the suit.
I don't know the article you are referring to, but something to the general effect of "The government did a bad thing" is not defamation either. Again, you have to cause demonstrable damages to an individual for them to win a suit against you. If the article was something closer to "The government did a bad thing, This is the person responsible, This is where he lives, Let's get him fired", or if the reddit comments were of that flavor (as they often are), the case for defamation is a little stronger.
Just for completeness, many former British colonies inherited criminal defamation from the general body of English common law. Apparently UK only repealed it in 2010.
Of course, Singapore is famous for actually using it, but still, in many parts of the world defamation can technically be a criminal offence even if in practice the legal risk is low..
https://en.m.wikipedia.org/wiki/Innocent_dissemination