Yeah, I think most of us would tell ourselves we'd violate the law, stand on our principles, and not send back the slave. But would we? Would it be right to do so? That was the law. The Supreme Court had spoken. Obviously, most people don't think that gay marriage is as big a deal as slavery--and of course it's not--but it is a matter of degrees at that point. If you would free the slave, then you are essentially acknowledging that there are times when the "it's the law and she should do her job whether she agrees or not" isn't absolute. What you are really saying is "it's the law and she should do her job unless it's really important." And to me, disagreeing with her about whether or not it's really important is a much weaker position than the "rule of law" one.
Obviously, if you are consistent like TW, this is not a hard question.
I would not really like it, but it is, or was, the law. If Dred Scott had brought his case while in a free state, he might have had a better argument. Waiting until he got back to Missouri was a losing argument.
At the same time, I would say to the residents of those states who did not like fulfilling their constitutional obligation to return fugitives from labor that they could always leave the Union. Then escaped slaves arriving in their state would be like slaves arriving in Canada: not liable to rendition.
Northern states wanted to have their constitutional cake and eat it too. They liked all the benefits of being members of the Union, but they did not like the obligations, which were a condition upon which the Union had been based in the first place. If they had left the Union, they would have been surrendering the benefits of Union, and would have gotten the freedom to not return fugitives from labor. Jefferson Davis noted this argument in his farewell speech to the Senate in 1861: membership in the Union comes with benefits and costs. Independence from it also comes with benefits and costs.
In this Kentucky case, while I believe the entire Federal judiciary s guilty of an egregious violation of its collective oath to support the Constitution, it has ruled and the people of the United States collectively and individually, have two options: leave the Union, or enforce the law (while, if you are really upset about this, trying to correct the judiciary's gross error through statute, amendment or impeachment).
