I'm not sure if I fully understand your question, but the title relates to Atticus's advice to Jem to "kill all the blue jays you want," but that "it's a sin to kill a mockingbird." Literally, Atticus believes it wrong to kill the songbird, which presents no dangers to corncribs or crops, unlike the blue jay; the mockingbird only sings for the enjoyment of its listeners. Symbolically, the mockingbird represents the theme of innocence in the novel, and several humans--Tom Robinson, Boo Radley and most of the children--are portrayed as mockingbirds. The death of innocent human mockingbirds, as represented by Tom's killing, seems much worse than the death of Bob Ewell, who only causes pain and misery to those around him. If your question centers around the idea of actually killing a real mockingbird, you must understand the temptation that a rifle presents to a youngster. As Atticus points out, most children will not be satisfied with shooting at tin cans; eventually, the target will become a live one. As a boy, I used to shoot at targets, cans, trees, etc., but I eventually took aim at live creatures. I once shot and killed a blue jay, and I felt horrible about it, because (despite Atticus's belief that they are harmful) I consider blue jays among the most beautiful birds on earth. I never shot at another blue jay--or bird of any kind--and instead took aim at squirrels, dragonflies (they really present a challenge because of their small size and constant movement) and the occasional snake. As for killing a mockingbird, I think that most people who would do so would not be happy afterward, for many of the same reasons presented symbolically in the novel. They are small, defenseless and harmless--a creature undeserving of "senseless slaughter... by hunters and small children."