Applying theories and decisions from foreign courts in U.S. law has long been a popular fad among liberal jurists and academics in America, especially by proponents of the "living Constitution." Left-leaning majorities on the Supreme Court have cited foreign court decisions and legal practices in several cases over the past 10 years to overturn centuries of precedent on a multitude of controversial issues such as whether minors convicted of serious crimes should be subject to either the death penalty or life imprisonment without parole.

In each case, concepts like the allegedly "evolving standards of decency," particularly in Europe, were cited among the reasons for reinterpreting the Constitution to prohibit what had previously been permitted. Conservatives on the court, particularly justices Antonin Scalia and Clarence Thomas, have opposed this trend, insisting that the use of foreign law to overturn the democratic process in the U.S. is intrinsically unconstitutional.

As Thomas wrote in Graham v. Florida, the 2010 case which barred sentences of life without parole for juveniles who commit crimes in which no one is killed: "Democracies around the world remain free to adopt life-without-parole sentences for juvenile offenders tomorrow if they see fit. Starting today, ours can count itself among the few in which judicial decree prevents voters from making that choice."

But it's the latest fad in European law that may ultimately prove the bankruptcy of relying on foreign standards of "decency": Euthanasia for children. Belgium's parliament on Feb. 13 became the first country to allow the process for terminally ill children of all ages (the Netherlands had previously approved it for children older than 12). The Belgian law requires counseling and parental approval before such a decision can be carried out, but it's easy to see how it could be used to pressure vulnerable, sick children into a deadly choice.

It's not just conservatives who worry about the likelihood -- and the moral consequences -- of such pressure. The left-leaning U.S. disability rights group Not Dead Yet vehemently opposes euthanasia and assisted-suicide laws. Eugene Kontorovich, a constitutional law professor at Northwestern University, says the new Belgian law also exposes the hypocrisy in the "evolving standards of decency" on which the legal left depends to rewrite centuries of settled U.S. law: children can't face the death penalty because they are too young and immature to understand the nature of their actions, but they're mature enough to decide when it's time to kill themselves.

In a Feb. 13 post for the Volokh Conspiracy legal blog, Kontorovich said that hypocrisy calls into question the Supreme Court's landmark 2005 decision in Roper v. Simmons, which outlawed the execution of minors as unconstitutional. The belief system on which Roper is based, he wrote, "is not one of paternalistic concern for youth. Rather, a system that permits the euthanasia of innocent 12-year-olds but not the punishment of guilty 17-year-olds is one that exalts autonomy without culpability."

It's a persuasive argument, and one which should convince U.S. judges to leave such foreign innovations where they belong: Abroad.