If adblocking is all about user choice then it's only fair that sites have choice to serve that content too. Right now it's incredibly hard for sites to reliably know if someone is using adblock.
Attempting to purposefully disguise that usage goes beyond any accepted ethics of using adblock today.
no that's not true - it's "easy", as long as you have cooperation from the advertising network. Their ads could do some callback onto the main page.
There are also constant updates to counter this. If you check the adblock forums, there are dozens of threads every day about how to get around checks on sites and even disable messages that specifically show up to adblock users.