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"
Cats and stray dogs often kill for fun, Orcas and dolphins as well... So intelligent life or life raised by very intelligent life seems to like killing other things...
Say, if for example someone is about to fly a plane into a Skyscraper, the cockpit door is closed tightly and you can't get in, even if the person is armed, you have a gun, you can kill the person and open the cockpit door... You would save many life's, in exchange for just one... Whats unethical about that?