Whilst people and businesses matter, if you ignore how they do something entirely, it does become purely ethical.
I use an adblocker only for malware protection, and pay many of the businesses I use online.
But I will always defend someone's right to use the content as they were given it. If you give away data, don't be confused if someone uses it in a different way.
Forbes appears to be finding a happy medium, or on their way. Such as disabling error logging caused by adblocking so that the user can have a decent experience.
Edit: And I must say, despite our differing opinions, this has been an extremely pleasant exchange