Do not be like Cain, who belonged to the evil one and murdered his brother. 1John 3:12, NIV
The Bible is so plain and simple about him, yet it has been my experience that there are often those who will defend Cain. The idea to them is that Cain did not get a fair shake. God had it in for him.
I remember a pugnacious young man in one of my classes who thought I was not being fair to Cain, as if I was the one who made up the story. It seemed to him like a personal slight that Cain was a farmer and did not please God with his gift, but was pleased with his brother's. The ire was directed against me because I agreed with God.
That Cain did not have a flock (supposedly) and gave of his produce, was inconsequential. Isn't a turnip as good as a lamb? That Cain could have bought or traded his crops for a suitable offering was not brought up. Cain defenders usually lasted for one class.
Besides the issue of Cain, you often meet those whose minds are made up as to what seems right to them. When they hear an idea from the Word of God with which they disagree, they strain to reconcile it with their fleshly mind set.
A pastor I knew struggled to reconcile the creation account with the classic geologic ages. He did not want to be found disagreeing with "science"! Had he studied even a basic course in geology, he might have found that the classic "ages" have been found nowhere on Earth, but are a hypothetical construct assembled to back up a ridiculous theory.
The vast Canadian Shield is composed of "old rock" overlaying "younger rock". But who knows enough to argue the discrepancy, or who even cares?
So it is that individual prejudices are opposed to the Bible. The motto for these is, "But I still say."