I get it, but the first thing to understand about message boards is that they have to make money or they won't exist.
I'd venture that 90% of posters use an ad blocker of some sort. You won't stop that. If even you block those users they won't turn it off...they'll just leave. It's the way it is.
So now that only leaves you with 10% or so of users that you can make money off of. Bigger, more prominent ads make more money, and there isn't really any other way to do it other than making this a pay board, and that won't fly either. Most people will also leave.
Full disclosure: I'm not compensated by HN and I have no financial connection with the site whatsoever.