We were taught to think that bad = criminal outlaw. If it's bad, there ought to be a law banning it and law enforcement to go after the perpetrator.
In Shadowrun setting (and generic cyberpunk setting at large), corporations are bad. Because of the aforementioned teaching, we tend to think that what they do must be illegal and that they just don't get caught for some reasons, like law enforcement and the government at large not doing its duty.
But it doesn't work like that. Corporations are legal beasts by nature. They do not break the law. What they do is have the law rewritten the way it suits them. And it may includes still having the government cracking down on anyone who does not respect the law (including the corporations who did not realize they were no longer in the alpha predator pack).
That's typically the case for everything extraterritoriality allow the megacorporation to do: they can have for free the government harassing all those A-rated smaller competing corporations for trying to do what the big boys do.
The thing is, it works with the "megacorporations" as a whole. Nine of the Big Ten may agree that, say, a 5% flat tax for megacorporation is the Right Thing to balance UCAS budget and fund Pentagon procurement plans. If the head of Renraku Americas tries to pay only 4.87% to proudly display a better profit margin than Renraku Asia at the big board, and get caught, he may find himself on the wrong end of a decision (or worst, a congressional inquiry) based on a report written thanks to intelligence anonymously handed over by other megacorporations intelligence services, backed by politicians whose campaigns were funded by these corporations, and covered by medias owned by them.