Swordfish were eaten by Jews in the Mediterranean countries for over 350 years. In the early 1900s they were also eaten in the U.S. In the early 1950s a prominent U.S. Rabbi paskened they were forbidden, and much controversy ensued.
Partly because the Conservative movement approved the fish, the Orthodox vehemently opposed it. This psak l’chumra was never accepted in Israel, yet as time passed fewer restaurants and stores were willing to sell it, and one cannot find it here anymore. Its scarcity contributes to the general feeling that it is tzu pas nisht. However, one can find yesteryear poskim who approved it.
In answer to LightBrite’s question, yes, there are a few well-known and some not well-known experts on this subject. When a company or individual wants to market a new fish or four-legged animal, the question goes to the experts at the OU, the Edah Chareidis, the Chief Rabbinate in Israel and Orthodox academic authorities to discuss the issue. Sometimes they agree and sometimes they do not. The aim is to achieve a consensus opinion one way or the other, cooperation which is good for klal yisrael.
All of the information above can easily be found online. I have access to one of the experts on these issues, so I have heard much of it from him.
I suggest avoiding attacking Rav Hershel Schachter, one of the truly great Torah scholars and poskim of our generation. It reflects very poorly on the attacker and displays great ignorance. When asked a question in learning or psak, Rav Schachter answers with full intellectual honesty. OU public policy and corporate considerations will not enter a personal discussion with him, and anyway, are governed by different rules.