WOO WOO WOO!!! TANG POLICE. PULL THAT 55G TANK OVER IMMEDIATELY AND REMOVE THAT TANG FROM ITS PREMISES...
I think the bottom line to this issue, is none of us has the right to judge what is right or wrong when deciding what's ethical in regards to which fish go into which tank. If you ask me, unless every fish in your tank is agricultured/tank-bred, you're just as guilty for putting ANY fish in your tank, as a LFS is guilty/liable for selling ANY fish to any aquarist, no matter what the compatibility/size issues are. Who became the Ultimate Saltwater Aquarium God that determined what the acceptable tank size was for a particular breed of fish? -- "Thou shalt not house any species of Tang in a tank less than 6 feet long", "Volitan Lions are deemed too big for a 55 gallon tank".
95% of the fish we keep in our tank were swimming in a vast and wide-open ocean maybe a week prior to us purchasing them. All of a sudden, it's OK to stick them in a 6 ft. x 2 ft. x 3 ft. tank, because some Marine Expert says is OK to do so. Now you can take the argument that many of the species we keep have just a small range in the wild where they live. Many varieties of clowns don't venture more than a few hundred yards from where they were born. However, everyone here agrees that Tangs, Wrasses, Groupers, etc. are open swimmers, and their range can be miles from where they were born. But the Tang Police vilify anyone who puts that species in a 55 gallon because "They need more swimming space". Are you actually going to tell me that an extra 2 feet is going to make that much of a difference to a wild Blue Hippo, who a week prior had thousands of miles of area to swim in? If you tell me yes, then I think you're all being a little bit hypocritical.