Flags are for content that's spam, off-topic, inappropriate. While you might claim that the content is dated, it would likely be better to post a comment providing a more recent source for the topic, not upvote the submission, and allow the community to decide for themselves what the best source of information is on the topic.
Flags are downvotes, given the lack of an actual downvote, and hence have much broader uses. What they should be used for is irrelevant to what they're actually used for.
Realize they are used as downvotes which is why using them as part of the ranking system makes no sense. Adding a downvote button also makes no sense. If you see something you do not want to see, but others do want to see it, click "hide" and move on.
That entirely depends on how you see yourself and other users as a member of the community. Do users have a way to influence what content the community has besides what they individually submit and upvote? Yes, flagging. Similarly with comments, we have more than one's own comments and upvotes, we have downvotes. Downvotes and flags both serve as useful signals to others what the community wants to discourage. Hiding / ignoring sends no signals, at least no different signals from never having seen the item at all.
This is a ridiculous position to take. The flagging operation is for things that violate rules and it severely punishes posts. It's not meant to be used as a tool for you to shove your opinions of what is worthy onto the community.
A post will die on it's own if it fails to receive upvotes. If you think something else should be on the front page, you go and upvote something else or leave a comment on the article explaining why it is crappy (comments down-weight an article). If you can't find something else that's better, then move on and stop acting like some gate keeper of worthy content.
If everyone behaved like what you're suggesting, the front page would just be a bland pile of the lowest common denominator content that displeased the fewest number of people.
The front page often is a bland pile of lowest common denominator crap. We couldn't even go a week without dumb political stories which are covered everywhere else (though charitably more because of miscommunication that it was meant to be an experiment and only a week long, still). Lots of people don't even look at it because they gave up, though I'm not exactly close to that point.
This is all beside the point that flagging is (no matter what it ought to be) an extra signal that has broader uses than merely spam/rule violating. I could also argue that "off topic", a use mentioned earlier and on the guidelines, is sufficiently broad and subjective that "something I think the HN community would be better off not discussing" fits "off topic". In any case the flagging mechanism is still there. The site does remove flagging privileges if you use it too often, so there is clearly a sense of how flags ought not to be used too often (or else you lose them) but that hardly influences why flags ought to be used.
