Earlier quoted context omitted.
90% of the whitelist is not paid, and that 10% helps develop the program. Not only that, you are asked upon installation whether or not to allow for acceptable ads (which is ticked on by default, but still not such a controversial point as you make it sound).
90% by lines or sites or 90% by money? ABP charges medium-sized websites through the nose -- and most startups qualify as medium-sized. Great business model, especially given that the filter lists are made by volunteers.
And the leverage by its users who do not get paid them. IIRC ABP gets paid around a third of the advertising revenue from whitelisting the advertiser if it reaches 10m impressions, so the more users seeing ads ABP has, the more money they make.