Generating value out of nothing and ripping people off are not necessarily incombinable things.
Nature is zero sum, economies are not valued in those terms because people prefer houses to trees etc.
But, be careful: http://www.smbc-comics.com/index.php?db=comics&id=2569
You can make this statement being true by moving your definition of "nothing" from economics to lay-people common sense, but then we'd be outside of a territory where we can obtain any actually reasonable observations.
> Nature is zero sum
What is "nature"? Observable universe from now to heat death of the universe? Yes. Earth in near hundred years? No.
> Robbery is also an economic transaction, and it can be positive sum if for example you don't notice.
What? How does the outcome of a transaction change depending on whether it's observed or not? Does it involve quantum particles of trees falling in the middle of desolate forests?
> That does not mean it's a good thing.
My comment didn't state anything about good or bad: these are very stupid terms and using them can't bring anything but loud voices and hurt feelings into a conversation.
If that were true nobody would ever feel ripped off. People irrationally engage in inefficient transactions all the time. For example, people who smoke cigarettes are more likely to be (and admit that they are) acting irrationally than truly deriving so much social or chemical utility from puffing on cigarettes that it exceeds the risk-weighted disutility of lung cancer, emphysema and so on.