I was reading about persecutions by Christians and was wondering if the persecutors justified their violence with passages of the bible and how they reconciled that with the teachings of Jesus.

In the below website i read about Calvin "So entirely was he in favour of persecuting measures, that he wrote a treatise in defence of them, maintaining the lawfulness of putting heretics to death"
http://www.wayoflife.org/database/protestantpersecutions.html