Why does scout say that if they didn't agree with Heck Tate's decision of how things happened that night it would be like killing a mockingbird?

Scout says this because Atticus was trying to blame Jem for the killing of Bob Ewell, even though there is clear evidence it was Boo. Atticus wanted to send Jem to court in order to show it was self defence even though he didn't do it. Heck Tate says Bob fell on the knife. If things went to court and nobody listened to Heck, it would show who really did it- Boo. Boo would be sent to jail and it would be like killing a mockingbird because he really wasn't doing anything other then saving the children.