Going by what is in the Bible, what has the Devil done that is so horrible?
The Devil in monotheism represents deception, or the source of "adversity" within existence, not a physical or anthropomorphic being.
The Devil is essentially, therefore, the challenge of the godly and of society to overcome in the "game of life" - one paradoxically therefore could view the Devil as "beneficial" - as without a Devil or "adversary" to overcome, there would be no reason de'tre to exist or enact social change and progress.
God destroyed almost every living creature on earth
God killed the first born children of Egypt
What has the Devil done of that magnitude ?
If one is atheist, they cannot logically assert and objection to killing, and for that matter, one could argue that materially speaking, nothing was "killed" anyway - as when one "kills" a human body, no matter or energy is actually "destroyed" - the material particles are merely arranged into a different form.
Or if for example, executing 1,000 homosexuals saved 10,000 from dying of AIDS, there would be no rational reason to object to the execution of homosexuals.
If on the other hand, one was a devout Christian, Buddhist, etc who practiced non-violence, etc they could potentially object to the mass-execution of homosexuals - but not the atheist.