If one engages productively with the site, rather than constantly complaining and accusing everyone else of being terrible, it is rather easy to pass the threshold of being able to flag comments.
If by "constantly complaining" you mean "turning up every few months to gawk at something particularly awful", then, well, that'd be really stupid, frankly. I am almost never on HN, so "constantly" is a poor description of anything about my behavior here.
Also: Why should i "engage productively" with a site full of people who are constantly (i use the word advisedly!) saying awful things?
Well, if you're talking about the karma threshold to be able to use the flag and downvote buttons on HN, it's really not that hard to reach that level.
One of my main use cases for HN is as a bookmarking service. I find something interesting, I post it with the bookmarklet. Same as I do with OneNote, except HN is faster. That's where the overwhelming lion's share of whatever collection of internet points I have amassed has come from. Frequently from the very least interesting of the articles that I post...
Just this week, I wracked up some ridiculous number of points from a throw-away release about Juypiter notebooks supporting F# that came up in one of the newsletters I get.
