I'm not necessarily opposed to it, I simply answered OPs question. It's unethical because there's no consent being given. However, humans do animal research regardless because they view it as "the end justifies the means", and they usually try to use humane methods (which is also not really an excuse because you can't ask the animal if it feels pain, or depression, or anything else).
To be fair, technically it becomes ethical when your position is that "the end justifies the means."
IMO Utilitarianism is a particularly dangerous ethical framework when wielded by narcissists who have a difficult time imagining that they might catastrophically fail (looking at you Sam Bankman-Fried), or might not be delivering salvation to the world (looking at you Elon, lol).
If you tell yourself it's for "the good of humanity", or the alternative is destruction / widespread death, you can justify any action.
