Greyball was actually a neutral tool that could also be used for good things. The regional managers of Uber could configure it to meet the needs of their market, so it had a variety of uses.
One example is that it was used to prevent taxi drivers in South American countries from targeting Uber drivers for beatings, car jackings or worse. Regardless of what you think about Uber or the taxi monopoly, it was a good thing to prevent physical harm to drivers on the service.
Even the supposedly bad uses of Greyball are, well, in the grey. Government regulators, often working at the behest of medallion owners (who generally don't drive taxis*), preferred to use fear as a tactic. They would target the drivers with whatever traffic tickets they could find, knowing that it is difficult for these drivers to fight. Greyball made this tactic harder, which forced cities into court directly with Uber, a much fairer matchup.
The really odd thing about greyball, though, is that there's actually no user requirement that the cars in the Uber app be real. They could have just "greyballed" everyone, and use standard anti-fraud practices to prevent someone requesting many trips and never starting them.
* Even where medallion owners are required to be owner-operators, they can often just sit in the taxi queue at the airport doing a crossword for a few hours.
