I am an Agnostic. Saying that to get it out there.
Have you ever considered that right and wrong were determined over generations of humans interacting with each other and figuring out what harms and what helps, what builds a safe and effective society, and what tears down and destroys one?
Also, add in the fact that what is considered good and bad is subjective, based on the particular culture of the people involved in its determination. Example, some believe killing apostates is good. Some believed in the past that torturing non-christians was a good thing. Also, women who knew too much about how to use herbs and other methods of healing were considered witches, and killing a witch was considered good. The funny part is all the examples I gave above were justified by them using their belief in a God.
Good can exist without a God, Evil can exist without a Devil. It is the consequences of the actions that determine which category it should be placed, not the doctrine of a religion. That is my take on the issue. Besides, there are over 4k religions on this planet, many also possessing multiple denominations. If there is a God that wants humans to believe in the one true Divinity, I would think a being that is Omnipresent, Omniscient, and Omnipotent could accomplish that with ease, and not have so much confusion on this present in the world. And no, the Devil is not a valid answer, because the devil is on a far lesser power scale than what many claim god is. It is limited in power, presence, and is nescient compared to God.
I don't expect a theist to accept anything I am saying, but I will not allow a theist to claim he has a full understanding of where our morality comes from either.