It’s similar to recommending slate star codex to someone. Unless that person is comfortable with rationally discussing uncomfortable topics, they will think you a nut job who supports everything on the site.
I'll talk about it in person with people I know at work or I'd mention it on my old blog - but I don't want to risk it to the "unwashed masses".
But maybe I'm being too cautious - it is pretty in-depht here. That alone might dissuade most of the shitposters. And the karma-requirements for downvoting seem sufficient.
More people mean a broader dilution of the level of discourse and knowledge, and greater and greater incentives to market / spam / propagandize.
ad free in the sense that there are no obviously in-your-face efforts at graphical marketing; HN is run by a strartup incubator and has a startup focus; flogging your latest release is the raison d'etre of the site.