Cold blooded killers aren't necessarily psycho and are often well balanced and rational in most facets of their lives. If they were all drooling, axe-wielding manaic types they'd be much easier to spot and round up. Willy was a logical, well educated man. The others on the lifeboat were more volatile, less sure of themselves, emotionally, politically, socially, morally. As to their lynching of Willy in the end, it's good to take into account that those who did so were hungry, thirsty, suffering from PTSD, to varying degrees, and, needless to say, very angry with him, and with good cause. They probably wouldn't have been so thoughtless and bloodthirsty had they been well fed, on dry land, not suffering from dehydration. The movie is about, among other things, people at war, under extreme stress, and how they cope with it. I think it's brilliant and provocative, wonderfully written and acted.