When you have no choice but to kill or starve, any killing is justified, but when starvation is off the table because you have access to agriculture and global supply chains, then that justification no longer exists.

I would expand the original statement to "there is no ethical way to kill someone who doesn't want to die, if you have an option not to kill them"

I consider cats unethical but the other animals get a pass.

Source: I'm a cat owner