Earlier quoted context omitted.
On a fundamental level, your server is free to do whatever it wants with the requests I send it, and my browser is free to do whatever I want with the responses it receives. Because your server is yours, and my computer is mine.
Is it easy to detect people who are using adblock and serve them nothing? Not that that is the best way to handle it but the OP does have a point. At least it would stop leaches. If you put content out for "free" because you make a few cents from advertising if they block the ads it's not much different than stealing.
For example, a year or so ago I saw that DuckDuckGo notices when you use ad blocking and very respectfully asks you to consider not blocking their ads.
A few months later, the ad blocking software that I use, added a feature to block those respectful messages too.
Note: I am not currently blocking ads on DDG