Controversial content (lately that means political) regularly gets flagged and removed. As a recent example the NYT Trump Taxes article went through cycles of being posted, rapidly upvoted, then flagged to algorithmic removal, over and over again. To point where meta-discussion came online (and was flagged) [1]

Personally I think downvoting is the appropriate response to say "this is not interesting or relevant to HN", but many have realized flagging provides outsized influence.

[1] https://news.ycombinator.com/item?id=24610890