There are many areas of the Christian life that believers can disagree about in good faith. These secondary and tertiary issues, while certainly being important enough to discuss and debate, do not qualify any Christian to be thought of as a heretic or asked to leave a congregation. Things like modes of baptism, church leadership roles, or styles of worship music are certainly convictions that we can argue over, but at the end of the day, those we disagree with are still our brothers and sisters in Christ.
One example of an issue that Christians today disagree about is the atonement. Now, I do not mean whether atonement occurred as a result of Jesus’ crucifixion and resurrection (it did indeed, and that would be more of a primary, salvific issue), but rather what the atonement primarily accomplished. There are various theories out there about the purpose of the atonement: the ransom theory, the moral influence theory, Christus victor. Perhaps the most prominent theory today (and the theory I find the most in line with Scripture) is called penal substitutionary atonement, which is essentially the belief that Jesus died on the cross as our substitute, paying the debt of our sins and satisfying the wrath of God so that we may be forgiven of our sin and deemed righteous in the eyes of the Father.
However, there are some who fall in the progressive camp that hold a very different view of the crucifixion. Instead of believing that Jesus’ death on the cross was a ransom payment, a victory against evil, or even a good moral example, these progressive “Christians” argue that the crucifixion was merely an act of “cosmic child abuse.” But when we look to God’s Word, we will find that, unlike the theories listed above, this specific belief about Jesus is heretical.