why does Atticus argue with heck Tate when Tate insists that Bob Ewell fell on his knife and killed himself?

The alternative would be to say that Boo was responsbile for Bob's death. Both men felt that Boo had been through enough, and his actions were based upon protecting Jem and Scout. Bob Ewell would likely have killed one of the children..... Scout's costume had been stabbed. Boo was merely an innocent, who stepped in to protect the children he loved.

As we know Atticus is a person with lots of justice he believes in fairness and feels empathy for others. Perhaps, Atticus thought that Mr. Tate was just trying to make up an excuse in order to not blam the murder on Jem because he’s a child, but Atticus as the person with lots of justice denies that fact and is afraid if he lied to them about that, for his families own good and not thinking about how others would feel, his children won’t listen to him because his children might become disappointed in him. He might’ve thought that he was not a good example to his children anymore because if he chosen to cover up it would show him thinking about his own families good being selfish. He tries to teach Jem and Scout throughout the story to jump into someone shoes and see their perspective. If he lied about something like this, this would be the exact same as lying to Jem and Scout on what he’s been trying to teach them. (He’s feeling empathy towards the dead Bob Ewell??? ._. The Bob Ewell who harrassed a lovely black lady, broke into Judge Taylor’s house, accused Atticus for taking his job, clearly holding a grudge against everyone who supported Tom Robinson during the trial, and almost killing his children... I’m not an expert of “To Kill A Mockingbird” I’m just a kid...Yes... I think Atticus thinks that Jem killed Bob Ewell it shows it on page. 365...)