I've often asked why people believe they and others "sin". I don't believe that because I don't see it.
Sure, there are bad people, criminals, people who set out to hurt others but most people are just trying to do the best they can to live a good life, take care of their family. They may make mistakes but I don't count that as a sin.
Then there's the other side of this question, which is personified by the incredible arrogance of thumpers, like the OP.
As guno pointed out, christians made up their god and they made up their devil. Its an imaginary, invisible bit of nonsense they're more than welcome to.
But the belief in a super-being does not somehow make you better than others and it most certainly does not qualify you to sit in judgment of others.
The Jesus you say you worship would abhor what the nutter thumpers have become.
Or it can be metaphor and simile – where ‘satan’ represents the evil men are capable of, and ‘god’ represents the collective good of humankind.
But there is no omnipotent extra-terrestrial deity that hears prayers, intercedes on the behalf of humans, and issues edicts of religious dogma, where transgressors are subject to some sort of punishment after death.
Likewise, there’s no malevolent extra-terrestrial deity that compels men to do evil, entices them to commit ‘sin,’ and is responsible for all that is wrong in the world.