> The site owner is saying, "Here, I made this cool thing. You can use it in exchange for $THING."

Name one popular website that explicitly states you can browse their website ONLY if you look at ads.

The notion that your users will look at ads isn't an obligation; it's an expectation. In contrast, wages are a contractually-bound obligation. It's not morally wrong to refuse to live up to someone's expectations.

If you owned a website, would you refuse to serve anyone browsing with Lynx? They sure aren't going to be looking at any ads.

But it's kind of a dick move to take something from somebody knowing full well that they expect something in return and then deliberately refuse to reciprocate.

Sure, if you're using Lynx, you really don't have an option. That's fair enough. But in many other cases, it seems disrespectful to me to use somebody's site and tell them, "No, you can't have anything in return for giving me this even though you clearly wanted to." You have the option of doing your part, but you decline to do so. That isn't how I like to treat people I appreciate.

I guess I basically just don't like mooching.

You're right, it is kind of dickish and it is inconsiderate on the user's part. I think we can agree on that. But I don't think it's fair to have such high expectations of your users. This is the internet, where everyone is an asshole and half the incoming traffic to your site will be wordpress logins. All we can do is hope the user is nice and will click on an ad.