As other commentors have pointed out, it’s vital that justice is applied as uniformly as possible in the interest of maintaining a fair and truly just system. Defense attorneys are an important check on the state and ensure (at least in theory) that it has met its burden in proving guilt before a person can be convicted, however heinous their alleged crimes may be. Without this adversarial dynamic prosecutors would be free to paint whatever narrative they please, whether rooted in reality or not, and any semblance of actual justice would go completely out the window.