Lamar: What Stopped Him?

No matter how many times I watch this movie, which I enjoy by the way, I am always troubled by Lamar and why he does not shoot Joe Kidd.

In the beginning, Lamar is shown to be a macho guy with a newfangled automatic rifle/pistol. He is prepared to show off to Joe by shooting out of the hotel window before being stopped by Mr. Harlan. After getting unceremoniously tossed down the stairs, he tells Joe that if it were not for Mr. Harlan wanting him around, he would shoot him. After the group rides out after Chama, Lamar mows down over a dozen of Chama's men in a display of his coldblooded nature. However, even with the provocation of getting tossed down the stairs, hit in the throat and punched out by Joe Kidd, when he encounters Joe alone and asleep in the back of the church, he hesitates and threatens Joe instead of shooting him then and there.

I know that Joe (Eastwood) is the hero of the film, but this plot point has always bothered me. I would think that Lamar would have been sufficiently motivated to kill Joe then and there in the church.