I agree the position I suggested is only a plausible assumption rather than a self-evident truth. Even so, I think it's a reasonable premise. Most people aren't going to use an ad blocker and then immediately leave your site just because of some related message, so I don't see the search engine issue as much of a danger. You might lose a few people who might have clicked on your ads if someone hostile spreads the word around, but firstly I doubt many people are really going to do that either (do you leave a web site and then immediately post on your blog/Facebook page/Twitter feed that "Site X Sucks!!!11!", really?) and secondly even if they do then I suspect the odds of converting anyone they tell who acts on that information are very low.