Adblock only exists because people/companies that advertise on the web have proven themselves to have no morals and no self control.
If the ads that were being served up weren't annoying, invasive, and occasionally dangerous, Adblock and its ilk wouldn't have gained any traction.
I guess I'm the only one who remembers going to a website and seeing more than one popup window, pop-under windows, ads that played sound at high volume as soon as they loaded, ads that slowed down loading immensely with large amounts of flash video, ads that captured your mouse cursor so you could play the "game" they put in their banner, ads that expanded to cover up the actual content of the page you were trying to visit, etc.
And that's not even getting into the ones that are actively hostile to your computer, spreading tracking cookies, spyware, adware, malware, trying to get you to install malicious programs, and so on.
Websites have to prove that they are trustworthy with the ads they serve up, then I will unblock them. I let ads through on GAF, I let ads through on Giant Bomb (even though this occasionally means annoying full page background ads on the actual website page), I let ads through on GameTrailers, and a few others. Everything else stays blocked until I see reason to whitelist the site.
Hell, even trusted sites like GAF occasionally let bullshit ads through on the desktop or mobile versions of the site accidentally, before they pinpoint where the awful ads are coming from.
Call me a thief all you want. I'm not putting my computer at risk by letting ads through on every website on the internet.
Bottom line, advertisers cannot be trusted. Therefore, Adblock.