Cultural practice is one of the lamest excuses ever invented to justify abhorent practices. If it's wrong, it's wrong, no matter how long the atrocity has been committed.
I have doubts about "Shark Finning" or any such practice being cultural as opposed to economic. I would hazard a guess that eating shark fins came from eating the entire shark and discovering the fin as the best part i.e. the tenderloin. I would even go so far to venture that the entire animal was consumed for centuries after the discovery that the fin was the choicest part, ala the Bison tongue and Native Americans.