I do not know what the long-term, indirect impacts are of helping to perpetuate a system of lies and injustice and subtle economic oppression, nor do I know how to calculate them.

Which part of the world do you work in? The USA? Western Europe?

If so, I would caution against assuming that the net impact of commercial lawyers is negative. Sure, lying and cheating. But probably less bad than no commercial law at all. And without commercial law, there would be no companies and no economy. The net impact of the economy, is, it seems, positive ;-0

I suspect that lying, cheating greed has a lot of negative emotional affect associated with it. By the time-honored rules of contamination of emotional affect to adjacent concepts, this must mean that the overall impact of commercial law is negative. But no, clearly it isn't, at least relative to the alternative of no commercial law. One must take care to only use emotions as evidence in domains where we have reason to believe that they are actually useful and accurate.

Also, remember that if you take a job in commercial law, you are not adding another commercial lawyer. You are merely replacing the person who would have got the job if you hadn't.