As others have said you must make your own decisions. For myself, I am not comfortable buying any animal unless I can reasonably commit to providing for it for its whole life. And, as somebody else pointed out, all fish are not the same. The ocean is huge and reefs are huge but there are many fish whose natural territories are 1-4 sq ft. (Clownfish and some gobies are what come to mind immediately but I would guess there are others.). Tangs swim miles every day. Even if I had an 8 ft tank I would never be comfortable housing a tang. On the other hand, I am very comfortable housing a couple of fish that have a naturally small territory. Especially captive bred specimens. My goal is to have a beautiful reef tank that showcases small fish in appropriate habitat. To me that's peaceful to look at because I know I'm not constraining the fish.