What are some good quotes through chapter 15-16 that prove that Jurgis's actions were unethical..?

If Jurgis' search for his wife is considered unethical (some today might think you don't check on your spouse). The following quote might work.

“No,” he answered. “But she hasn’t come home—and I thought she would be here the same as before.”

“As before?” echoed Jadvyga, in perplexity.

Jurgis then checked on Ona at her place of employment.

"But the man had seen that the boss was watching him; he started on again, pushing his truck. "I don't know anything about it," he said, over his shoulder. "How should I know where your wife goes?"

Abusive to his wife.....

"An instant later he leaped at her, as she lay groveling at his feet. He seized her by the throat. "Tell me!" he gasped, hoarsely. "Quick! Who took you to that place?"

Attacking his wife's attacker.....

"He was a big, red-faced Irishman, coarse-featured, and smelling of liquor. He saw Jurgis as he crossed the threshold, and turned white. He hesitated one second, as if meaning to run; and in the next his assailant was upon him. He put up his hands to protect his face, but Jurgis, lunging with all the power of his arm and body, struck him fairly between the eyes and knocked him backward. The next moment he was on top of him, burying his fingers in his throat.

To Jurgis this man's whole presence reeked of the crime he had committed; the touch of his body was madness to him—it set every nerve of him a-tremble, it aroused all the demon in his soul. It had worked its will upon Ona, this great beast—and now he had it, he had it! It was his turn now! Things swam blood before him, and he screamed aloud in his fury, lifting his victim and smashing his head upon the floor."