There is substantial evidence to suggest that the NBA should like having one or more so-called superteams at any given time. Superteams tend to elevate superstars, like Magic and Bird in the '80s and Michael Jordan in the '90s. This is a superstar league, and higher global profiles for the very best players draws more attention to the NBA itself. Legion are the stories of international fans who watched '90s Bulls games at all hours of the night just to catch a glimpse of His Airness. (A number of these fans have become NBA players and speak fondly on those memories.)
Ratings spikes tend to follow the creation of superteams. Jordan's Bulls won six titles in eight years and had a 72-win season; the NBA's television ratings never reached a higher level than during that run. The 2010-11 Miami Heat brought with them a huge ratings bump, even though (unlike the Bulls) that team was widely reviled. People love a spectacle, and that's what superteams are. The Warriors maintained high ratings and sold out every road game last season while chasing the regular season wins record despite not becoming villainous until the playoffs. Adding Kevin Durant will only boost the interest level more.
The NBA, as a single-business entity that is focused on maximizing exposure, benefits from the creation of superteams. But the NBA really isn't a single-business entity. It's 30 smaller businesses working to each maximize their own revenue.
It's true that a rising tide lifts all boats, but it's also true that winning in the NBA is a zero-sum game. Winning has a huge effect on revenue for those individual teams. Studies have indicated that winning percentage has a strong positive correlation with attendance. Gate receipts are a huge piece of the revenue puzzle for individual teams, as are the knock-on effects from a higher gate: more merchandise sold, higher arena operations revenue for concessions and parking (some of which is shared or taken whole by the team), higher demand for other games through smaller supply of available tickets.
If a few teams are doing all of the winning, are they creating a higher tide that lifts all those less fortunate boats, or a tidal wave that wipes them out? That's the concern those teams have, and that's why NBA commissioner Adam Silver is down on Durant joining the Warriors.
As we tend to think of the NBA as a single, massive business concern, we tend to think of Silver as concerned primarily with growing the league's total footprint. But really, Silver answers to 30 bosses. It does him little good to grow NBA revenue as a whole if only a few teams are truly benefiting. The Warriors, thanks to the wealth of their ticket-buying fandom and their incredible success, were drawing eight-figure gate receipts for single playoff games. Some of that is shared with the broader league. Half ends up in players' hands. The rest stays with the Golden State Warriors, helping to fuel their next talent coup (Durant), a coup that hurts the revenue potential of another team (the Oklahoma City Thunder) directly and other teams indirectly.
Consider it this way. There are 1,230 wins available in an NBA season. With perfect parity, every team would go 41-41. Now introduce just one outlier. Give one team -- say, the Warriors -- 73 wins. With perfect parity for the rest of the teams, they'd go 40-42, a little bit worse. Give one team 73 wins and introduce two more outlier teams that win 65 apiece. The rest of the league is now down to 38 wins apiece. Teams that win 38 games don't really capture the imagination like teams that win 40-something games.
This is a facile example, as the NBA has nothing close to perfect parity (in fact, quite the opposite). The league's standings are messy in permanence. But the larger point stands: when a high-quality team gets better on the court, that starves the other 29 teams of a) a talent asset that would help each of them get better, and b) potential wins, which are necessary in most cases to maximize local revenue.
Adam Silver's dream isn't really about perfect parity. It's about 30 fandoms that are excited enough about their teams to open their collective wallets and pay to see those teams 41 times a year.
The immense financial success of the Warriors is good for Adam Silver, and important. But it's also important that the Dallas Mavericks succeed financially, that the L.A. Clippers and Washington Wizards and New York Knicks and Portland Trail Blazers and Sacramento Kings and Charlotte Hornets succeed financially. A few teams hogging all of the success for themselves will eventually starve the rest, and when you are starved, you get desperate. That's not what Silver wants or needs. He wants and needs to spread that cake around.
The most intuitive way to spread it around is through robust revenue sharing. The league has gotten better (much better) on that account since the 2011 lockout, but those high-revenue teams come to that solution only begrudgingly.
So Silver and his crew turn toward ways to level the playing court in opportunity to succeed financially. Ensuring all teams have equal opportunity to win basketball games is the clear route to that end. Superteams are roadblocks on the path.
That's why Adam Silver wants to prevent them, no matter how attractive they are to the wider viewing audience.