When it was my turn I approached the bench and handed my questionnaire to the judge. He looked it over, noted my "Yes" responses, and asked me why I couldn't be fair in this case. I responded that I could not be fair to the prosecution because I was in favor of an adult's right to buy/sell (under the condition outlined above)/use drugs, and that I thought all drugs should be legalized right now. …On the one hand, you shouldn't lie. On the other hand, if every potential juror followed a policy of truth, then drug defendants would be tried only by jurors who think drug laws are hunky-dory.
The judge told me it was fine if I favored drug legalization, but asked me if I would be able to uphold the law as written. I said I could not on moral and ideological grounds, and said to him, "There's no way I would find this defendant guilty as charged."
With that the judge thanked me for my honesty (which surprised me) and told me I was dismissed from further service (which did not).
I have no problem with disregarding the value of honesty in a case like this. By creating this untenable choice, the state has forfeited any right it might have had to your truthfulness. But while lying in this situation is morally justified, it's not morally required; as philosophers would say, it's supererogatory. You might choose to lie in order to assist the hapless defendant, but by doing so, you would also be placing yourself in danger of prosecution -- possibly just trading one injustice for another. You'd be sticking your neck out for a stranger with the possibility of great (and arguably comparable) personal loss. In general, I don't think a workable moral code can command everyone to make that kind of sacrifice, but it can specially commend those who do.