Had you asked me a few years ago, I would have shown you my own site (but is now defunct due to adblock + the economy at the time). I ran a gaming website that started out as a small hobby, but ended up being incredibly popular within its audience.
The primary/initial function of this site was to serve up dynamic images that depicted a user's activity on the gaming platform it catered to, for use on Forums, blogs, and social networks. I went on to serve other data-based content, such as extensive leaderboards (globally, as well as searchable by game, by country, or both), user stat profiles, and other platform-specific info.
In return for access to the platform's data to make this all possible, I had a legal agreement with that company that said that I could not directly charge for access to the features of my community site. Advertising was the only viable solution for maintaining it. While there were a few missteps on advertising (Yahoo (for its short-lived ad platform) sometimes pushed adult-oriented ads), I was generally good to my users in that regard, eventually becoming popular enough to serve relevant ads from gaming companies and related lifestyle products (they won't talk to you unless you have x number of users/page impressions).
My costs were infrastructure. I had several servers creating/serving those remote images, handling static site images, storing and organizing user/gaming history in the databases ... I had to hire consultants when the site outgrew my limited-at-the-time knowledge of data modeling and querying. Advertising helped me scale both up and out, and I ran it for nearly 6 years. By necessity, I gained a LOT of skills during that time.
About 5 years in, Adblock had started to become popular beyond the technical crowd. It's always been a set-and-forget thing, and we didn't have a lot of the fancy detection tricks we do now, so there was little I could really do. I was breaking even for my hosting (several hundred dollars a month for nearly a dozen servers; and that's WITHOUT bandwidth costs, because I had a great relationship with my hosting provider)... but couple that with the economy crash, where the advertising that WAS getting through wasn't paying much, and I ended up paying out of pocket for nearly a year before it was just too much.
What started as a small project in which I expected just a couple of people to use ended up with 5 million users, and small notoriety within that gaming circle (including several magazine stories). Advertising directly enabled me to scale. I was unemployed when I had first started it, and had to hop a number of inexpensive hosts (which weren't inexpensive when you have no income) because I'd outgrow their limits in a week or two. Sometimes, advertising is simply the best/only option available.
Advertising is not inherently evil; people have been paying to get their message out for hundreds of years. Actively boycott the sites/networks taking advantage of its users, but don't damn the entire system.