Oh, Wars. Wars Wars Wars. You so crazy.
Gangs in 2020 aren't "evil", but they are typically violent, short-sighted, selfish antagonistic social elements. Still, some are a positive influence on their neighbourhoods and are appreciated. Back Alley Brawlers. Think 2020 Guardian Angels.
Boostergangs are a different matter. With very few exceptions, boostergangs take all the fun of being a gang member..and then cyberpsychosis it up. Not all are cyberpsychos, of course, or they'd be unmanageable and shortly thereafter, destroyed by their neighbouring gangs, police and well-armed locals in some horrific multi-casualty battle.
They do run very low on the Humanity scale, their black-market cyberware having made them more violent, more aggressive, more inclined to do really crazy shite. Boostergangs are why the Combat Zone is a no-go area for most Police units and why nights in Night City are still so very dangerous.
There are less directly violent boostergangs, like the Braniacs, for example. Hated by all the other boostergangs, they are more indirect.
There are more than just Boostergangs in Night City.
There are 'dorpher gangs. Wild Things, for example. Not overindulgent in cyberware like your boostergang, instead these fun fellows indulge in different chemical cocktails, the most popular being Dorph, endorphin-based combat and pleasure drugs.
There are prankster gangs, like the Vampyres and, arguably, the Bozos. There are combat gangs, protective gangs and poser gangs.
But the worst, the most violent, the least predictable are the actual boostergangs. The Slaughterhouse. Maelstrom. The Blood Razors. Borderline or worse cyberpsychos, they kill for fun, steal when bored and profit from blood. Too few to typically present a threat to real corporate power and a handy distraction for the population from the abuses of said power, Boostergangs in Night City represent the near-epitome of the feared cyberware abuser.
The only thing worse, the only thing more senselessly, horrifically violent than a boosterganger is a full-on Cyberpsycho, and there's a few of those scattered in the boosters as well.
Anyone interested, all this information about gangs and Night City can be found in PDF form here:
http://rpg.drivethrustuff.com/product/589/Night-City?it=1 for all of two cups of fancy coffee, $8. It's a great read and one of the best sourcebooks for any game, ever. Check it out.