that is a perfect example. They feel like they are doing the right thing, but in reality they are not aware that they are going against God and the order of the universe, or whatever. The Roman people, the Jewish people, of that time that Jesus was killed, had no idea what they were doing or who the man on the cross was. But even then, Jesus asked for their forgiveness.
The only part of the New Testiment that Jesus advocated violence was throwing the money changers out of the temple. Your can ignore the book of Rvelations because it hasn't happened yet and will only come about because Humanity messed up so badly that Jesus had to come back to fix things. But anyway, true Christians would not have gotten involed in the Cruisades, the Inquisition, because Jesus did not advocate those things. It was a mistake made by Christians of those times. They did not know what they were doing, they thought they were doing good. But in reality they gave Christianity a bad name.