CATES. It isn't as simple as that. Good or bad, black or white, night or day. (I, I, 139-40)
Bert's attitude is very threatening for some people, especially if they believe that being principled means dividing the world into right and wrong. What do you think?
RACHEL. Mr. Drummond. You've got to call the whole thing off. It's not too late. Bert knows he did wrong. He didn't mean to. And he's sorry. Now why can't he just stand up and say to everybody: "I did wrong. I broke a law. I admit it. I won't do it again." Then they'd stop all this fuss, and—everything would be like it was. (I, II, 267-72)
Rachel wants Bert and Drummond to go against their principles in order to avoid the spectacle of the trial, and the possibility of a jail sentence for Bert. But these two characters are having none of that. Rachel, unlike Bert and Drummond, is motivated by fear. She would rather things be unfair than to rock the boat.
DRUMMOND. […] Cates, I'll change your plea and we'll call off the whole business—on one condition. If you honestly believe you committed a criminal act against the citizens of the state and the minds of their children. If you honestly believe that you're wrong and the law's right.
Then the hell with it. (I, II, 332-37)
Here, Drummond is making sure that his client is all the way on board with his strategy in the trial. He's a principled man who knows his client is technically guilty, so he's going to try to show the jury that the law itself is unjust… if Bert agrees.
CATES. (Quietly, with determination) No, sir. I'm not gonna quit.
RACHEL (Protesting) Bert!
CATES. It wouldn't do any good now, anyhow. (I, II, 346-51)
Bert is a stubborn guy. Even with a nice girl like Rachel tempting him to back down and plead guilty, he sticks to his guns.
DRUMMOND. […] Bert, whenever you see something bright, shining, perfect-seeming—all gold, with purple spots—look behind the paint! And if it's a lie—show it up for what it really is! (III, 96-99)
This image of a flawed rocking horse exemplifies Drummond's understanding of his mission in the world: he's a truth-seeker, someone who calls it like it is, and shows all of those pretty-painted but rotten-to-the-core ponies what they're up against.
CATES. […] (With difficulty) I feel I am…I have been convicted of violating an unjust law. I will continue in the future, as I have in the past, to oppose this law in any way I can. I— (III, 264-67)
You can't keep a good man (or dog) down. Even after his loss, Bert lets everyone know that he'll continue to fight for what he believes is just—and that's to teach modern science to future generations of children.
BRADY. (Thundering) Your Honor, the prosecution takes exception! Where the issues are so titanic, the court must mete our more drastic punishment—
DRUMMOND (Biting in) I object!
BRADY. To make an example of this transgressor! To show the world— (III, 295-305)
Drummond and Bert aren't the only ones with principles. Brady, too, is planning to take this battle all the way to the bitter end. He wants to reveal Bert as a sinner who's waging some sort of unholy war against the Bible. Yeesh.
DRUMMOND. Just a minute. Just a minute. The amount of the fine is of no concern to me. Bertram Cates has no intention whatsoever of paying this or any other fine. He would not pay it if it were one single dollar. We will appeal this decision to the Supreme Court of the state. Will the court grant thirty days to prepare our appeal? (III, 306-12)
In this passage, Drummond lets everyone know once again that this trial wasn't about keeping Bert out of prison. He won't be satisfied until the law that put Bert on trial is changed. He's ready to pursue this case to the bitter end.
DRUMMOND. You don't suppose this kind of thing is ever finished, do you? Tomorrow it'll be something else—and another fella will have to stand up. And you've helped give him the guts to do it! (531-35)
Dude. So Drummond believes the purpose Bert's trial wasn't just to highlight the injustice of the law against teaching evolution. He wants to inspire other free-thinkers to stand up for what they think is right. We're imagining a whole new generation of Drummonds matriculating to law school right this very minute…
RACHEL. Mr. Drummond, I hope I haven't said anything to offend you. You see, I haven't really thought very much. I was always afraid of what I might think—so it seemed safer not to think at all. But now I know. A thought is like a child inside our own body. It has to be born. If it dies inside you, part of you dies, too! (Pointing to the book) Maybe what Mr. Darwin wrote is bad. I don't know. Bad or good, it doesn't make any difference. The ideas have to come out—like children. Some of 'em healthy as a bean plant, some sickly. I think the sickly ideas die mostly, don't you, Bert? (III, 575-85)
Finally, our girl Rachel starts to think for herself. Here, she's basically saying that pursuing the truth—be it right or wrong—is more important than feeling secure in what one already knows. Way to go, Rach.