Non-human predators that hunt, kill, and eat other animals...do you consider them unethical, or is it only unethical for animals capable of inventing the concept of 'ethics'?
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"