Ask not "Why kill the alien?" Rather, ask, "Why not?"
This user began as playing a Russian fan-cracked X-COM: Enemy Unknown version for Windows Mobile 5 known as POCKET UFO. In v1.25 it didn't have the "arm grenade" function.
Although he got annoyed, he also is stubborn enough to be back for more. He just wishes there is adjustable difficulty. Because he is a noob.