THE BIAS TOWARDS SIN CONTRADICTS THE DOCTRINE THAT GOD HAS A GOOD PURPOSE FOR US
 
Sin is an act in thought, word, deed or ommission that is against the moral law of God. Sin should not necessarily lead to more sins.  Eating quinoa once has nothing to do with leading you to eat it again.  So if sin leads to bias that must be God's fault.  Religion says that sin leaves a bias in the sense that a sin leads to more sins and makes new sins easier to commit.  

How could God want us to be compassionate and allow suffering for that purpose when he allows so many strong and convincing temptations to sin and even ensures that any sin will lead to new temptations and create them?

If sin is virtually the same as having a bias to sin then how can we trust and forgive sinners?  Love the sinner and hate the sin would end up being a mere outlook and impractical.  It would not be the first principle we have that we have to have but not for practical reasons.  But it would prove religion cannot claim to be able to to do anything about hating sinners.

Sin is even punished by an attraction to sin and self-destruction - a sin deserves the punishment of you developing a bigger attraction to sin.  No system of retribution or justice or punishment goes as far as wanting to see people corrupted by their crime sin or anybody else's. Justice is about taking a stand against evil and the evil person not encouraging the evil which would be revenge pure and simple.
 
The Bible teaches that the fall of man from happiness and holiness when Adam and Eve sinned was a real fall (page 65, Arguing With God) and was a terrible thing and that God did not want it. This tells us that discipline is no excuse for God permitting our suffering. God never wanted Adam and Eve to undergo it and did not think that Adam and Eve needed to work with suffering beings to be good. God should not have let Adam and Eve spread their evil by having children but should have made billions of Adams and Eves and put each pair of them on one planet by themselves with the animals so that there would be fewer sinners. The fall doctrine makes God out to be extremely cruel and stupid.

Christianity says we are all biased towards sin since the time Adam sinned (Romans 3) which was why Jesus described the road to salvation as a narrow and rough one. This view contradicts the Christian claim that we must think the best of everybody even if their behaviour looks dodgy. When observed, you will see that the average Christian does not really think the best of everyone.
 
The notion that we are that sinful does not ring true to most people. That is because most people see sin in humanitarian terms - wilfully hurting other people. But when sin is seen as not giving God enough love though he deserves it all for he makes our whole being it becomes clear that everything or nearly everything we do is a sin.

The humanist view is that we must avoid condemning sins that are not sins and regarding deeds as evil or bad when they are not. Anything with too many moral rules is not moral at all. It only makes people feel less confident about being good.