For instance, the effect was that Goldman lost money, while some other guys made money - what's the harm here ?

Moreover, the trade being busted, the guy that initially made the money, probably found himself in a very uncomfortable position, since chances are he already covered his risk and hedged the lucky trades. So overall, he lost money just because Goldman was able to force the rules in their favor.

Unfortunately, markets are rigged, just as most things -> the bigger you are, the more influence on the rules and how they are applied you have.

If the little guy makes a mistake Goldman will happily take the money. If they make a mistake the rules need to be changed. This simply is not right.