In what way is Mr. Underwood's editorial in the Maycomb Tribune similar to Atticus's advice to Jem and Scout when when they got their guns?

What do you mean Caitlyn?

“Remember it’s a sin to kill a mockingbird.” That was the only time I ever heard Atticus say it was a sin to do something, and I asked Miss Maudie about it.

“Your father’s right,” she said. “Mockingbirds don’t do one thing but make music for us to enjoy . . . but sing their hearts out for us. That’s why it’s a sin to kill a mockingbird.”

Look for the similarities;

"Mr. Underwood didn't talk about miscarriages of justice, he was writing so children could understand. Mr. Underwood simply figured it was a sin to kill cripples, be they standing, sitting, or escaping. He likened Tom's death to the senseless slaughter of songbirds by hunters and children, and Maycomb thought he was trying to write an editorial poetical enough to be reprinted in The Montgomery Advertiser.

How could this be so, I wondered, as I read Mr. Underwood's editorial. Senseless killing-Tom had been given due process of law to the day of his death; he had been tried openly and convicted by twelve good men and true; my father had fought for him all the way. Then Mr. Underwood's meaning became clear: Atticus had used every tool available to free men to save Tom Robinson, but in the secret courts of men's hearts Atticus had no case. Tom was a dead man the minute Mayella Ewell opened her mouth and screamed."

In both of these excerpts the "killing" is considered senseless; there is no reason to kill a bird of song who does nothing except to make you smile, and there's no reason to kill a man senseless just because someone says he's done something........ killing a cripple is wrong, that Tom hadn't done it was obvious, but the editorial and the feelings behind it are all correct. He was dead from the moment Mayella opened her mouth, and his death was senseless.