Probably a signal that the user base does not find those issues interesting.
Snowden because it's nothing we don't already know, and refugees or gender politics because they always degenerate into political (i.e. not interesting) mud slinging matches.
On a side note, if a community with the general high quality and good moderation of HN can't have a good discussion on those topics online, I'm inclined to believe that having same is just plain impossible.
Personally, my thought process upon seeing one of these articles is something like:
1) Ugh, another one. Let's check the comments..
2) As expected, a dumpster fire. Nobody even RTFA. Let's look at the article..
3) Nothing even remotely new or interesting. Who voted this up? Flag.
It's far easier to manipulate systems than it is to accurately reflect either your typical reader viewpoint, or an intelligent and informed viewpoint. This is a classic failing of any democratic system, election balloting included.
Early "democratic" systems were often anything but -- about 14% of Athens' citizens could vote, and about 6% of the US at the time of George Washington's election. There are arguments for a broader electorate, but they come with distinct problems.
Vote brigading in particular is a standing issue on almost all online moderation systems. Some sort of trust cascade might help. It's what, say, the US electoral college was meant to provide initially, though how much of that function remains (and how it might manifest) is rather in question.
As for Snowden, a counterpoint is that some people see this as an issue which requires constant reminding. Advertising and propaganda both work through repitition, and sometimes the truth gets a chance for that as well. There's certainly enough repeat traffic on other topics at HN. (Though yes, many of those get beat down in the submission queue.)
Of the article isn't interesting, the article wouldn't have been voted up.
Marking down the comments indicates a desire by some to to enforce groupthink. Why? Because many people use votes to indicate agree-disagree instead of a quality metric.
I think it's harder to agree/disagree with the typical headlines featured on HN. Most articles on HN appear to be straight.
But let's say that two articles were in the queue, one pro-X, the other anti-X and the pro-X forces were dominant. Sure the pro-X article would hit the FP, but the anti-X forces would still comment on it and be down voted.
Also the bias is only visible in the comment section because down voted comments remain visible, whereas a down voted article gets flushed down the memory hole.
Just because you want to argue about politics with people doesn't mean that people want to argue about politics with you! Maybe they do, sometimes, in some contexts, but if the social cues (i.e., downvotes) indicate otherwise, then maybe not at that time and place. There's nothing wrong with people not talking about stuff they don't want to talk about.
Also, internet forums have learned over multiple decades that otherwise interesting discussions can easily get derailed by people screaming at each other over unresolvable issues. If the community doesn't keep a lid on it to a degree, the quality of discourse goes into a downward spiral that it can never recover from. It attracts people who just want to argue about stuff and it drives away people who want to have interesting discussions. This has been seen time and time again, in newsgroup after newsgroup, mailing list after mailing list, web forum after web forum.
Holding back that inevitable decline is like fighting against entropy- if it stays popular, HN is almost guaranteed to decline, and become more and more like Slashdot circa 2010, right before it poofs out of existence and/or relevance. But if users actively push back against the tides of forum entropy (i.e., discussion getting drowned out by arguments), a forum can at least have a nice long run before that happens.
I think what people want to avoid on HN is the sort of discussions where people are just asserting hot takes back and forth to no other end than the act of publicly asserting hot takes. This was never fun to watch on Crossfire or First Take or whatever, it's not fun at awkward drunken family gatherings, and it doesn't fit in with the vibe of HN. It's invigorating to the participants but much less interesting to read, and for every poster there are hundreds or thousands of readers.
That applies to online forums just as much as it does to real life, some forums are just more focused than others (just like some households are way louder, more chaotic, and have more drama than others). Almost every place other than HN thrives on arguments, so at least there are plenty of places to have them.
