Some cultures eat octopus, some eat dogs, some eat cats, some eat cows, and of course some eat humans. And some eat vegetation. Do you honestly think those cultures sit back and question what they are doing and if it is ok in order to survive?!
I'm laughing at the responses to this post - sentience, history of eating octopi, god told me, etc.. as an excuse for why humans shouldn't eat octopus. Who really fucking cares.
I can ramble on and debate all this until I'm blue. My goal is not necessarily to argue, but to light a spark.