Earlier quoted context omitted.
This brings up another case for detecting AdBlock: if you think your users are receptive to whitelisting non-annoying ads, you could detect the plugin and let them know that you strive to incorporate ads in a non-intrusive way and kindly ask them to disable AdBlock. Edit: sounds like this is what reddit does. Props to them!
Many sites do this, but the problem with Adblock that most people are not happy about is that it AUTOMATICALLY blocks everything. You have to whitelist, and most people just turn adblock on and leave it be... If it was required to blacklist instead of whitelist it'd be better. Many sites with non-intrusive ads are being blocked because of this and that's detrimental. It's already hurting many businesses to the point…
I, as a user, wouldn't be happy having to blacklist all sites.
I won't pay a monthly fee for most sites, because I read a little on a lot of sites - I don't mind paying a 1 penny per article fee if it is convinient.