The issue OP seems to have is that while “X damages the environment” is a claim that science is reasonably well equipped to answer, “X is unethical” is not.

While scientists claiming that farming octopuses is damaging to the environment falls within reasonable scope of their work and expertise, them claiming that it is unethical may not be so, yet the author is lumping both together in the same introductory sentence.

>Should the author not write their own opinion from their own ethical context, but rather keep it to themselves, since other cultures might disagree?

Yes.

At a minimum, they shouldn't state their "own opinion from their own ethical context" as some kind of universal fact: "it's not only deeply unethical (...) scientists say".

What earthly purpose would that serve? They're scientists; they subscribe to a moral system. Subscribing to an ethical system involves arguing it through rhetoric and reasoning. Scientists are only expected to be politically neutral; they're not Uatu the Watcher.

The problem here is the misleading implication that there is a singular set of correct ethics, hidden behind a false appeal to scientific authority.

Don't the vast majority of people think there is a singular set of correct ethics? Why do you think otherwise?

The mere fact that there is wide disagreement about some ethical questions doesn't help the argument (as some people think), because there are all sorts of very controversial questions where it's still commonly accepted that these questions have a correct answer.

>Don't the vast majority of people think there is a singular set of correct ethics? Why do you think otherwise?

No, the vast majority of people don't think there's a singular set of correct ethics, and especially not one where "eating octopus is unethical" is a tenet.

> Don't the vast majority of people think there is a singular set of correct ethics?

I agree that maybe most people believe in objective morality, but moral relativism exists and I don't think that it's so unpopular that it's insignificant.

https://en.wikipedia.org/wiki/Moral_relativism

>What earthly purpose would that serve? They're scientists; they subscribe to a moral system.

The moral system is unrelated to their scientific advice.

It also doesn't cover the "don't eat X animals" part, as even for their society (e.g. USA) that's debatable ethically, and not something the generally acceptable moral system holds.