If one looks at a scriptural account of what constitutes evil, one will find that there are essentially two major categories:
In category 1 we may find abominations like eating shellfish (Lev. 11: 10-12), touching pigskin (Deut. 14:8), or interacting with a menstruating female (numerous accounts). In other words, the kinds of things we all realize have nothing to do with evil or being a decent fellow.
In category 2 there exist laws like “thou shall not kill…steal…bear false witness…commit adultery” (from The Ten Commandments) and so on. These are those things which we all (save the psychopaths among us) realize are bad and that we strive, through to the present day, not to do.
Scripture being the confused, contradictory mess that it is, one often finds the case that category 1 sins make no sense and category 2 sins are occasionally sanctioned in order to meet some immediate religious end. In Biblical texts, one finds God sometimes stepping in and giving murder the thumbs up provided that the victims are adulterers, witches, Gentiles, your enemies’ babies, or people who talk back to their parents or who are caught working on the Sabbath. In the Old Testament God doesn’t merely look the other way, He actually commands acts of murder and genocide against sinners and unbelievers and, as often as not, against civilian bystanders. Beyond the OT, one finds similar behavior in the Qur’an. The opening story of the Book of Mormon finds the initial protagonist, Nephi, being commanded by an angel to behead an unconscious man (1 Nephi 4).
There are a few conclusions to be drawn here.
First, we don’t get our morals from scripture.
Our moral sensibilities are not derived from scriptural texts, rather we bring our morals with us when reading scriptural passages, and actively filter the ancient teachings through our modern understandings of right and wrong. Were this not the case, we would find the faithful in Nevada burning suspected witches and dashing their babies against rocks, believers in California slaying the livestock of their Wiccan neighbors, and god-fearing residents of Maine going straight gangbusters on the shrimp and lobster industry. This illustrates clearly that believers have chosen to uphold some scriptural commandments and cast others aside. Therefore we see that there is some higher moral code that is brought to the study table, and that this code is applied to scripture, not derived from it.
Second, scripture authors confusion about what constitutes evil.
“Thou shall not kill” is a nice sentiment, but in scripture (supposedly our source for learning God’s will) it is both preceded and followed immediately by divinely sanctioned genocide, assassination plots, and terrorism. If God is able to step in and change the rules on a whim, then a God-based moral system does not, in fact, provide us with anything approaching a grounded or stable morality. There is no clear reasoning behind it that we can discover, and no consistent textual reference. A God-based moral structure offers only a turbulent and mercurial system that is unintelligible to humans.
Third, not all evil is created equal.
The sorts of acts that are called evil that fall into the “duh” category are those things which have stood the test of time. The very reason that they fall into that category are because they are as evident to us today, perhaps even more evident, as they were a few thousand years ago. That category is set apart from the behavior in the “LOL” category, where there are laws proscribing such acts as wearing a cotton-polyester blend t-shirt (Lev. 19:19). In one category, we have a list of things which cause grave human suffering, and in the other we have a list of things which might have provoked feelings of disgust in some people, in some time period. Disgust, a subjective experience, is something that is in constant flux across time and cultures, but suffering (also subjective) is constant.
Suffering, on its own, is universally considered to be a bad thing for those who experience it. This is why the only stable morality that we can ever possibly have is one based upon
a) the reduction of suffering, and
b) the promotion of happiness
Cause no harm, try to do good. This is what a reliable morality is based upon, not the whim of an indecisive, capricious being whose plans are ineffable or incomprehensible.
It’s not that you should throw away your God-based morality, it’s that you need to realize you never had one and move on. #Duh