No one is forcing anyone to whitelist the site and view the DRM'd content. The site is simply offering an explicit choice to the user: go away or play by our rules. Whether or not serving the ads in the first place is morally correct simply does not matter—the price for admission could change to require the user's car, their livelihood, their life, and the premise is the same. There's an explicit acknowledgement of the cost and a conscious choice by the user.
An apt analogy would be a magazine on a table with a sign denoting the price. Without FuckAdBlock, the sign reads "Price: ___". Taking the magazine and not paying anything isn't immoral, it just shows you value yourself above others (nothing wrong with that). With FuckAdBlock, the sign now reads "Price: Your kidney". By taking the magazine and not paying, you're quite literally stealing, regardless of the price now on the sign.
