Based on what assumption? Is there any documentation stating that yellow tangs were poised to go extinct if the ornamental fish industry were to continue to harvest them from the ocean?
This is the distinction that needs to be discussed, and always gets dismissed because we equate captive breeding to being the better choice. It's not that simple. There's a lot of politics surrounding this as well as manipulation from the industry to pull on the heart strings of the hobbyist in order to get buy in that spending more on a captive bred fish somehow means you did your part for sustainability. When in fact all you did was pay more for a fish in order to perpetuate a business model that has little benefit for existing.
Emphasis on the bold text above. You are not wrong with your opinion but in all honesty there is nothing wrong with promoting captive breeding and or raising marine ornamental fish or aquaculture corals and rock. Likewise there is nothing wrong with promoting sustainable collection with reduced impacts on the reefs around the world.
Both sides are guilty of promoting their respective narrative. Wild are brighter, captive are weaker and duller, etc. While most of us understand the politic or "feel good" side of things one has to ask the bigger question has the ban actually impacted the hobby? If so, in what way other than what the hobbyist sees as it relates to price or availability.
This talk always generates a lot of controversy I agree regardless of ones view. My personal take is that this conversation needs to happen sooner and among the respected businesses who have more at stake. Otherwise it will happen by the respected governments for them.
Hope your day is well.