When Basil visited the widow...

Basil in the film was a bookish and ineffectual person. He was shy, withdrawn, and inhibited. He wrote about human emotions but perhaps did not experience or even understand them. In the novel, the narrator ("Basil" in the film) told the reader that he was having so little real contact with people that, if he was asked to choose between making love with a woman and reading about it, he would have chosen the book! Zorba was the exact opposite. In one scene in the book, the narrator asked Zorba why he did not write about his rich experiences, and Zorba's answer was that a person who lives his life to the full would not have time to write about it. In the film, when Zorba saw Basil for the first time, he already noticed that Basil was always "calculating" and weighing all the possible outcomes before taking any actions. So what Basil did with the widow was quite consistent with his character.

In the film, before Basil slept with the widow, there was one earlier scene in which he was shown going to her house at night and she told him to go away. He tried to pass her a note, which fell to the ground, and as he tried to retrieve it he was stopped by Mavrandoni. My interpretation is that the scene was not “real” but instead showed Basil’s imagination on what could have happened if he had really gone there. You see, he was always worrying about the possible outcomes of his actions. In his own words, he didn’t want any “trouble”. Zorba was quick in pointing out that life itself means trouble and there is no way to avoid it. At the end, it appeared that Basil accepted (well, at least partly) Zorba’s philosophy.

The character of the widow was rather underdeveloped in the film (and also in the novel). You called her “a devout, and devoted widow”, but actually it was not so clear. In the book, one character called her a brood mare that started to whinny as soon as she saw men. I believe she, just like Dame Hortense, had seen better times. She had to live among these uncouth, ignorant villagers but felt herself to be above them. Everyone in the village desired her but she rejected them. Nevertheless, She needed a man just like any woman in her situation would, and Basil was the obvious choice. You said that Basil could have paid her normal social visits, which would be true if his intention was courtship probably followed by marriage. But in the film, I don’t think either Basil or the widow envisaged a long term relationship. You don’t expect him to follow “normal visiting hours” when what he wanted was sex. You may say that was wrong, but it explained why Basil chose to approach her stealthily at night so that no one would know.

You argued that Basil’s action caused the widow’s “social protection and respect to vanish” leading to the horrible outcome. It was true that in relatively primitive rural societies, it was usually taboo for a widow or unmarried woman to be sexually active. But in the film, ultimately the problem was that everyone (and not just Mavrandoni’s son) wanted the widow but she rejected them all. They were hostile to her from the very beginning. An earlier scene, in which they were needlessly cruel in hiding her goat to make fun of her, was particularly revealing. When the young man committed suicide, that was used as a pretext not only by his father but also by the other villagers to take revenge on her. I think the other villagers would have stopped at stoning and humiliating her. While in those days lynching was not unknown in many parts of the world, it was against the law and so in a way the horrible outcome was probably not foreseen by anyone. In the book, after the killing, Mavrandoni fled to the hills and became an outlaw.