Why does Scout say telling the truth would be "sorta like shootin' a mockingbird"?

At the end of chapter 30, Sheriff Tate indirectly tells Atticus that Boo Radley is responsible for killing Bob Ewell but refuses to disclose this information to the community in order to protect Boo from receiving unwanted attention. Sheriff Tate tells Atticus,

"To my way of thinkin’, Mr. Finch, taking the one man who’s done you and this town a great service an‘ draggin’ him with his shy ways into the limelight—to me, that’s a...

At the end of chapter 30, Sheriff Tate indirectly tells Atticus that Boo Radley is responsible for killing Bob Ewell but refuses to disclose this information to the community in order to protect Boo from receiving unwanted attention. Sheriff Tate tells Atticus,

"To my way of thinkin’, Mr. Finch, taking the one man who’s done you and this town a great service an‘ draggin’ him with his shy ways into the limelight—to me, that’s a sin. It’s a sin and I’m not about to have it on my head" (Lee, 280).

Atticus then looks down and Scout and asks her if she understands Sheriff Tate's reasoning, and Scout responds by metaphorically applying Atticus's early lesson concerning why it is considered a sin to kill a mockingbird. Scout tells her father,

"Well, it’d be sort of like shootin‘ a mockingbird, wouldn’t it?" (Lee, 280).

Scout's maturity and moral development are displayed when she metaphorically applies Atticus's lesson. Scout perceives Boo Radley as a symbolic mockingbird because he causes no harm, shares his joy with others, and is a defenseless being. Scout understands the true meaning of her father's lesson, which emphasizes the importance of protecting innocent, defenseless beings. Sheriff Tate knows that the attention Boo will receive from the community will cause him discomfort and purposely protects Boo by keeping his involvement a secret.