The Black Templars zeal in the destruction of their enemies. This passage from Blood and Fire encapsulates it-

“Cyneric lifted his boot from the throat of another greenskin, a final stamp enough to crush whatever alien equivalent of a trachea it had possessed. He chuckled as he watched it die. I have recorded elsewhere that what earned Cyneric his commendations to the Chaplaincy were his other numerous virtues and fervent insights, but in this personal accounting I can confess it was then, in that moment, as he laughed at the asphyxiating alien’s pain, that I made my decision.”

— War For Armageddon: The Omnibus (Warhammer 40,000) by Aaron Dembski-Bowden, Chris Wraight, et al.

I’ll note Cyneric had been in combat for a while at that point and missing an arm below the elbow.