“Congress big-footed its way into the Terri Schiavo case...”
The purpose of government is to defend the lives of Americans.
Terri Schiavo was starved to death by order of the Florida judiciary.
The federal government has a DUTY to “uphold the Constitution” and to “protect and defend life.”
The federal government has a DUTY to uphold the Constitution and to protect and defend life.
While the federal government does have the duty to upheld the U.S. Constitution, there is NO provision in the document that orders the government to "protect and defend life", as you put it. That is a matter left for the states, under the 10th Amendment of the U.S. Constitution.
I'm sympathetic to your zeal in defending "life," but every time the federal government gets involved in the issue, it turns into a big mess, in which we lose more and more of our liberty. State's rights, remember?