You can believe that "the devil" is the reason why so many bad things happen in a world ostensibly governed by an all-powerful loving god.
Or you can declare there is no such thing as the devil and bad things are just god's way of letting man have free choice.
Unencumbered by facts and evidence, you can believe anything. There really is no limit.
And why not? We all end up just as dead, but if you lived your life believing in fanciful ideas, maybe you had a happier life than you otherwise would have.
Just don't try to force that on other people, because it makes me sad when I see people believing nonsense.