The thing about technology (mainly when it comes to computers and the internet and what have you) is that people really want things to be free. They don't want to pay to search, watch, chat, or anything, and for the most part, they get their way; most sites have at least some version of a free service, like Dropbox. The part that people fail to realize is that -believe it or not- it does cost money to do these things, so they put advertisements in their free products.
It just astounds me that people want (a) a free product with (b) no advertisements. They want to have their cake and eat it too. Actually, they want to have two cakes, eat them both, and then not give any cake to the people that gave them the cake.
Anyway, it just doesn't work that way. Sites and services want to make money; that's kind of the whole idea behind why the authors/developers do what they do. But people tend to forget that, and just focus on themselves: they don't want advertisements. How dare an ad appear on my page! So they install Adblock Plus or edit their HOSTS file or what have you, effectively blocking 99% of the ads that pay the developers of the sites they use.
Do not get me wrong, there are many times I want to block ads and I believe that it is just, like talking ads, ads on sites that are just link-baiting, and sites (particularly blogs) that have at least 5 different ads per page, and have their articles spread out over multiple pages. There are also some gray areas, like ads in Youtube videos (Come on, Google, having 3 text ads per page plus all the partnerships you have doesn't pay for it already?), but otherwise, little text ads here and there don't bother me. No, I don't click on them, almost ever, but the fact that they are there is fine with me.
Google itself is an advertising company. They release a free web search, email, blogging platform, photo managing site, and much, much, MUCH more, and all they ask in return is that they advertise. (I'm not going to get in to Google tracking you to advertise more effectively; advertising can definitely be abused.)
On a quick side note, it's funny also how easy it is to tune advertising out on the web. It's very easy to (subconsciously) train yourself to ignore that part of the page on Google, Gmail, or Facebook. But beyond that, ads are so amazingly lame. They're like tiny little infomercials, and no one takes them seriously unless you are a fool.
One site that does advertising right is DuckDuckGo. I realize that I kind of pimp DDG alot, but I swear I mean everything I say. DDG is the first site where the ads actually catch my eye because they are more than just empty words, and the sites that advertise there seem to be strictly higher quality of anywhere else I've seen.
So on a closing note: choose either $ or ads, some sites do advertise intrusively and should be banned from the internet, and DuckDuckGo has amazing advertisements.