I have two problems here:
First, from what I can find, the average click-through rate online for ads is something like 2%. I suspect it's even worse for smaller blogs and independent sources that don't advertise using Google.
Let's assume you're getting a dollar every time someone clicks on an ad. I think that's high, but whatever. If we were to get everyone to start paying for content, that would translate to it costing around 2 cents for you to look at a page. If you're reading 30 articles from your favorite site every month, that's 60 cents a month. So people talk about how expensive content would be, but from what I can see it probably wouldn't take a huge amount of money to give sites the same amount of support that they're getting right now.
Secondly, I think it's at least a little bit problematic to say that ads make content free. The only reason why any company would ever pay to put an ad on someone's content is if they expect to make that money back, either by encouraging consumers to buy a different product than they normally would have, or by encouraging them to buy more of a given product than they otherwise would have. Statistically speaking, you are paying for content that is ad supported. If you weren't, nobody would put ads on that content.
And I realize that sounds a little bit like splitting hairs, but I get tired of this idea that ads don't have a consumer cost. If you completely get rid of ads through ad blockers, and by not listening to radio or watching live TV, and by not using any service that doesn't give you a purchase option... it will not take long until you become re-accustomed to "normal" levels of advertising. And once you are accustomed to that, you will immediately notice on venturing back into the ad-filled world just how much time and attention and mindspace that ads demand from you.
Everyone believes that they're atypical, and that ads don't encourage them to spend more, or to buy branded products instead of generic ones, or to treat practical products like status symbols. Most people are wrong about their own abilities though. Most people are affected by advertising. That doesn't mean that advertising is evil, there are lots of good use-cases for advertising -- but it does mean that ads aren't free.
It would be very hard to gather data on this, but I suspect that if you tracked the average spending habits of people who were inundated with ads, their monthly spending would increase more than the cost of buying a few magazine subscriptions. I suspect that's even true of most people on Hackernews. If anyone has data, they're welcome to prove me wrong though.