I disagree. The fact that congress is working against the spirit of the original authors by constantly increasing the length of a copyright, does not in my opinion reflect on the legality of the law in question. Perhaps you can say that the goals of the legislature are unconstitutional, but the laws that they are passing do not, by themselves, seem to violate the constitution. Because the law explicitly states a limited length for the copyright(assuming the copyright owner is not immortal), it is in compliance with the limited time-frame provision in constitution.

The letter of the law does not conflict with the constitution, but the intent of the legislature conflicts with the intent of the founding fathers. I think that it is more appropriate for this issue to be addressed in the legislature than in the courts.