Some just don't read the bible nor have gone to church I know this isn't exactly considered bias, but quite a few atheists (but not all atheists) tend to take bible verses and use them to support what they believe about christians or god's existance. The only problem is that they tend to use the way they view the bible/christianity in order to interpret those verses.
For example, I once heard someone say that Leviticus 20:13 ("If a man has sexual relations with a man as one does with a woman, both of them have done what is detestable. They are to be put to death; their blood will be on their own heads,") shows that christians want gay people to die/christians hate gay people when:
1. The verse only talks about people who ACT gay, not people who ARE gay
2. The verse is a law of ancient isreal and is intended only for isreal (leviticus is an account of ancient laws of isreal set forth "by god"), and not many christians follow the laws of ancient isreal anyway (we sometimes eat bacon)
3. Even though the bible says acting gay is illegal, the bible also says to love everyone countless times throughout itself.
All I'm saying is that Atheists tend to look at different parts of religions such as christianity and interpret them without actually understanding the religion itself or the way the believers of the religion interpret the religion and the religion's texts itself.