While Congress clearly has the authority to regulate federal court jurisdiction, and to provide for such jurisdiction so as to ensure that state courts act within constitutional constraints, I feel the legislation is inappropriate on several grounds. First, state courts make these sorts of decisions all the time in life-or-death situations, including death penalty cases without equivalent federal interference. Second, this creates a terrible precedent for ad hoc federal interference in high-profile cases of injustice. Private relief legislation is rightfully disfavored. Third, after-the-fact efforts to [undo] state court judgments are also a bad thing. If Congress wants to use this case as the basis for new legislation to provide for federal court jurisdiction where state courts violate incapacitated individuals' federal due process rights, that would be fine and dandy. Unprecedented ex post facto challenges to state court judgments, on the other hand, should be avoided -- even when the cause is just (and, yes, even when a life may be at stake).
This raises a point I've been meaning to make. On the conlawprof email list, I've taken the position that the statute is constitutional, and I do think that. Congress has power to define federal jurisdiction, and, though it can't violate individual rights or require the federal courts to do things beyond the bounds of the "judicial power" (as defined in Article III of the Constitution), it can provide for all sorts of intrusions on the work of the state courts. It's important to recognize that state courts can violate constitutional rights and that Congress can provide for the federal courts to protect individuals from various bad things state courts might do.
There is an argument -- made in the federal court case -- that the federal statute does violate individual rights. The theory is that it burdens Terri Schiavo's right to refuse medical treatment. But assuming Congress really did have the power to pass its highly specialized law, that scarcely makes it a good idea.
Even if a court should not find the statute void because of its lack of deference to the state courts, Congress ought to have given more consideration to the work of the state courts. And even if the statute is constitutional despite its singling out of one person for special, positive treatment, Congress ought to have felt constrained, knowing that it would not routinely give special treatment to other persons like Terri Schiavo. Its unwillingness to write a general law betrays a lack of commitment to any principle -- principle demands general applicability and not favoritism. And don't tell me it was too much of an emergency for it to be possible to draft a generally applicable law. Terri Schiavo's case has been around for years.
Congress acted in a bold, emotive fashion that showed too little respect for the serious, hard work of state courts. After the spectacle of this case, however, I tend to think there will be political pressure on Congress not to behave this way in the future. And this legislation is a monument to Congress's susceptibility to political pressure.
UPDATE: Sam at Disability Law agrees: "There is ... no good argument that the statute is unconstitutional. But that doesn't mean the statute is a good idea."
ANOTHER UPDATE: Stephen Bainbridge struggles with the conflicts among four principles he agrees with: the culture of life, limited government, federalism, an the rule of law. And more, about federalism, here.