I'm unsure about how I actually feel about this.. on the one hand, blizzard already offers cheats for single player. And a powerful world creator which can give you any kind of gameplay experience you want..
So the only reason I can think to hack the game is to boost achievements, which at first glance seems odd, but I cheated in one of my 360 games to get achievements for it (In my defense, it wasn't as easy as just putting in the code and bing 1000 gamerscore, it took me a solid week while cheating to get them all).. so it'd be hard for me to be critical against these people..
On the other hand, I doubt I would hack a 360 game to get achievements.. I only utilize cheats that are in the game, and the bugs sometimes associated with them. My Dragon Age Origin achievements show that I did the level up glitch at some early point (in actuality I never used that character to beat the game, but you wouldn't know it to look at it), and I used a level up glitch for the specific purpose of getting achievements in Fallout 3 the day before I had to return it to blockbuster (which also is hilariously blatantly obvious cheating in my achievement list)..
So yeah, i have a history with cheating to get achievements.. But I think the crux of the matter is.. if the developers patched those glitches out of the game, I wouldn't get butt hurt... I think if blizzard had made glitches that allowed for easy achievements, I'd probably use them... but if they patched them out I'd say "oh well, that was fun while it lasted" and work for them legitimately.
So I think that purposefully creating glitches in the game to make achievements easier to get and then getting butthurt when blizzard decides that they want to "patch them out" (It's not what they're doing, I get that, but it's what they SHOULD want to do, if it were possible), I think that's sort of silly.
Banning is the wrong move. Wiping achievements, that I can understand, suspending from multiplayer games, that I can understand. Something to say "We don't like you doing this, we caught you doing this, here's a slap on the wrist".. Make it a painful slap, but just make it a slap. Banning people from playing a single player game is a HORRIBLE precedent.