I think people are getting confused about price fixing and US law. There is no statute that makes it legal, it is an interpretation by the Supreme Court of anti-trust laws that prohibit anti-competitive behavior.
In 1911, the US Supreme Court ruled price fixing was illegal and that was the status of the law until 2007. The fact that manufacturers may have terminated retailers during that period does not mean it was done legally.
All of this changed in 2007, when in a 5 to 4 decision, the court reversed itself. In ruling that price fixing is not automatically illegal, the court relied on the argument by economists that resale price maintenance agreements can promote competition depending on the circumstances. Now, instead of price fixing being automatically illegal, courts must apply a case-by-case approach to assess their impact on competition. That doesn't mean that resale price maintenance agreements are legal in all instances.
The most common argument in favor of price maintenance is to enable a new producer to break into the market by getting retailers to carry its product. Without resale price maintenance the retailers won’t incur the risk of stocking and promoting a new product, or so the argument goes. The theory is more producers equals more competition at the top of the food chain and ultimately consumers benefit. There is also an argument that consumers benefit when retailers who provide product demonstrations and other consumer services are protected from internet based discount pricing.
Of course what we see in the scuba industry is that it is the most established manufacturers that engage in resale price maintenance, not the new guys. There is therefore at least some question as to whether ScubaPro and Aqualung agreements would pass muster under the new law.