As a defence lawyer, I've sworn an oath to try to get the most favourable outcome for my client by any legal means necessary, so if I or any of my colleagues used peremptory challenges to get a less favourable outcome, I'd be calling up the law society probably, and maybe you guys want to do the same.
That's why I take issue when we hear about how the Crowns misuse them. Misuse that is discriminatory use should be prohibited and regulated. There are no perfect ways to do it, but there are ways.
One of the fundamental principles of our adversarial system is that you have two opposing adversaries, both with their own interests. Now, the Crown has a bit of a different interest, as the Minister of Justice is not exactly a fully partisan litigant, but the point is that you have two opposing interests and you're going to get a fair jury. I sometimes sit there when the Crown says, “Oh, I really wanted that person on the jury”, and the Crown probably feels the same way when I exercise a peremptory challenge. The point is that you have balance. I'm going to hope it's most favourable for my client. That is my ethical duty, and the Crown is going to do what it can to present the best case it can, and obviously present the evidence. It's that balance of the two adversarial sides that hopefully produces a fair result.