Referring to your comment in answer to Joseph Wiessman's question (in comment), Legitimacy in ethical reasoning is also quite subjective. Your example of the Nazi camps is a particularly poignant example where those who could did engage in barbarism and cruelty from our point of view, yet legitimized their actions based on their own views perhaps that their prisoners were considered animals and a belief that they might have deserved nothing less. History shows us that the Allies won the war, the Nazi's didn't, so it's a moot point as to which point of view was subjectively more correct given we do not live today under the influence of years of further historical cruelty had the other side won, and that thankfully neither you nor I were taught in school to accept the Nazi point of view.
Your assumptions that such behavior is "wrong from the start" is ultimately formed from a cultural and historical perspective. So to are the behaviors of Sunni vs Shiite Muslims in Saudi Arabia. You and I might not agree with the way in which the Arab world live, but neither do they agree with our way of life. We see much of their approach to corporal punishments and their treatment of women to be "cruel" and immoral from a certain point of view, yet from much of the Arab world's point of view, we are meant to be the immoral ones.
When it comes to corporations in our own countries on the other hand, the waters get a little muddier, and perhaps from our own moral perspective, a little dirtier. There seems to be a collective forgetfulness among the heads of really big corporations. They know ultimately that they have people building their products in places they wouldn't want to know about, yet they take no responsibility for any cruelty committed in such places because as far as the corporate heads are concerned, it was someone else's problem. They can argue that 'it was a subsidiary', they were 'outsourcing', and that if it happened in another country, then that outsourced labor happened under the jurisdiction of another country's labor laws. The corporate heads don't have to know, don't want to know, and therefore they don't feel a need to concern themselves about such matters. You and I might think that their moral compasses are a little out of whack, but for these very rich and powerful individuals, that's beyond the realm of their concern.
If on the other hand the "cruel sweatshop" was discovered in their own back yards, you'd likely see a very different story, and depending on the individual either genuine concern for the well being of individuals loosely connected to them, or perhaps concern that they might get in trouble, and so behave as expected in order to cover their backsides. Again a lot of very individual and subjective reasoning is going to occur there.
I guess that the point I'm trying to make is that these corporations supposedly exist under our laws, and most likely governed by individuals from similar cultural backgrounds to ourselves, so to us their actions (or lack thereof) might seem to be out of the norm, or perhaps even worse to us because it may seem to attack the fabric of our own core beliefs.
As to which philosophical school of thought all of this falls under... nearest I can get it to is perhaps Kantianism or Deontological.. but perhaps one of the more well-versed students of philosophy might be able to come up with a better match for you.