Blizzard banning people for cheating in SC2 campaign

[Raistlin]

Please, don't try to patronizingly argue legality without knowing the law.

You pay for the game yes but you play the game in accordance to the bindings of a contract that is what a terms of service (or End User Liscence Agreement - EULA) essentially is it's a legally binding contract between you and the program developers saying you agree to play the game by their rules. If you do not accept the contract then you cannot install or run the program and can contact the developer of the program for a refund on it should you choose to.

I would advise you to read what I've already stated about the contracts issue. This is wrong. They cannot throw whatever terms they want into a ToS that you don't have access to until after you buy the game (which is when the contract actually originates) and call it all a contract. They do it anyway, they make you click the "I agree" button after you don't read it anyway, but any unusual terms in there are not going to be legally enforceable.

Everything you said after that was equally wrong, but I want to address one point:

In most TOS or EULA contracts there are multiple clauses that state essentially you won't illegally without permission from the developer modify their program in any way. Now whilst some developers won't hold you in breach of contract unless you start to make a profit from the modifications you make to their programs it is perfectly legal for them to hold you so if they choose to make a point.

Breach of contract requires more than that. It also requires a showing of damages, which is another reason this is legally dubious. The valid purpose behind any "non-modification" clause is to prevent hacking which in some way, shape, or form harms Blizzard. Broadening its meaning to affect the way single-player users enjoy the game violates a lot of contract principles, even if a court found that this was a breach, such as the implied covenant of good faith and fair dealing and unconscionability.

Achievements are not just a number next to your name for many gamers

This is irrelevant and also hypocritical. Just as I can't tell people how to treat achievements, you also can't tell people how to enjoy a game. And they could just remove any "cheaters" ability to win achievements, which is plenty feasible since 1) they already do that for in-game cheats, and 2) they are able to detect this game-modifying programs somehow, or else these people wouldn't be banned.

EDIT: Which brings me back to my main point here, which is that regardless of the legality issue, this is a retarded thing to do. We can set the contracts issue aside. Hell, for the sake of this argument -- and so I'm not forced to read any more horrible misunderstandings and perversions of contract law -- I will even assume what they're doing is 100% legal.