If anyone is really over-represented, its Libertarians, who will sound like right-wingers when a Democrat is in office and like left-wingers when a Republican is in office
I'm not sure which libertarians you've seen posts from here on slashdot, but I have yet to see one that looks like a left-winger when the GOP is in power. Most slashdot self-described libertarians that I come across just don't want to be branded by the GOP, and lean on their copy of Atlas Shrugged as being somehow proof that they are stunning individualists.
well-reasoned arguments will get voted up, and worst-case I get to see what other people with different political beliefs than mine consider a persuasive argument.
That said, I was trying to describe more so the articles that make the front page here than the discussion and the comments in them (and how they are moderated). We've seen a noticeable up-tick in pro-GOP front page articles in recent years and a noticeable down-tick in articles of any other political slant. 2017 has been a slight exception to this, only because we elected a professional internet troll to the white house last November. Prior to that we never made it a week without seeing at least one blatantly anti-Obama article on the front page here while it was rare to see one article that was celebrating him in a month.
When I had trouble was the final stages of the 2016 election. All appearances were that the comment/moderation system here got pwned by Russian trolls, with the result that the stuff that got upvoted bore no relationship whatsoever to the quality of the thoughts
I have a hard time believing that the Russian trolls would have found this site to be worth their efforts, unless they were using it to train bots. Slashdot's user base has been steadily shrinking over the years (in terms of how many users actually comment on anything or partake in any kind of discussion). If the Russian trolls had paid any attention to what makes the front page of this site they would not have found it worth their while either, as they were trying to push the election in favor of Trump and this site was happily touting how awesome he was anyways.