Indeed. Sites seem to think that people want adverts and will click on them willingly - in a world where advertising is saturated and people do not like them. Therefore some sites don't rely on people clicking their banners but take money from advertisers who will put whatever they like there, porn, viruses, etc which are paid "per hit" on the site. That is shit we don't want to have on sites, malware. Therefore I too keep Adblock and disable adverts - I don't want them, I don't need them and I don't want malware; sites that moan about having blocked adverts can kiss my butt.
What sites are you visiting?! In my experience it's usually because that's how the sites earn money. For me personally, the sites that complain about AdBlock are tight-knit communities much like this one.