Easy, one argument response: The user should be in control of the code executed on his computer.
Couldn't the same argument be used for the blizzard bot? One is more intentionally telling users to break the TOS, but at the end of the day the user is running the code.
In the case of Blizzard, this would mean forcing gamers to run clients that were known by Blizzard to not contain bots; for example, Blizzard could force users to use signed client binaries. Blizzard might actually be able to get away with this because their users are paying customers who really, really want to play their game.
In the case of a website running ads, this would mean forcing viewers to run clients that were known by the website to not contain ad blockers; for example, the website could force viewers to run signed browser binaries. Of course, no site that runs ads will try this, because it would just mean nobody would view their site. Notice that sites whose users actually need to go there to do business, such as banking sites or Amazon, don't complain about ad blockers. It's only sites whose business model depends on ads that do. That should be a "here's your sign" moment to ad-supported sites that their business model is not sustainable. It should not be an excuse to sue ad blockers.