...but they are not. Sure it happens less frequently but once is too much.

Warren
Lee Hill, a man with a mental disability currently on death row in a
Georgia prison, is scheduled to be executed on Feb. 19 despite a Supreme
Court decision outlawing capital punishment for criminals who are
mentally retarded.
On Feb. 5, the office of state Attorney General Samuel Olens released a statement confirming Hill's execution date.
From the release:
On
February 5, 2013, the Superior Court of Lee County filed an order,
setting the seven-day window in which the execution of Warren Lee Hill
may occur to begin at noon, February 19, 2013, and ending seven days
later at noon on February 26, 2013.
Hill, who was sentenced to death
for the 1990 murder of Joseph Handspike, had his execution halted in
July after he made an appeal based on Georgia's recent switch to a new
execution method, which involves the injection of a single drug called
pentobarbital -- a drug often used for euthanizing animals. (Previously,
the state had used a three-drug cocktail for its lethal injections,
according to The Associated Press.)
But on Feb. 4, Hill's chances of survival were dashed when a State Supreme Court judge struck down his appeal.
Superior
Court Judge Thomas H. Wilson ruled in July that Hill met the criteria
for mental retardation by a “preponderance of evidence” but found that
Hill did not meet Georgia’s strict definition for mental disability.
Georgia
is the only state in the country that requires mental disability to be
proved beyond a reasonable doubt, the New York Times notes. Hill’s
lawyer Brian Kammer told previously told The Huffington Post that his
client's IQ was rougly 70, and that his mental capacity peaked at the
development of a sixth-grader.
Although the Supreme Court case
Atkins vs. Virginia ruled in 2002 that executing prisoners who are
mentally disabled violates the Eighth Amendment, the ruling left it up
to states to define who falls into that category.
As Think
Progress points out, only the Supreme Court can stop Hill's execution at
this point. The Supreme Court, however, refused to review Hill's case
in June.
Both The New York Times and former U.S. President Jimmy
Carter have advocated on Hill's behalf, saying he shouldn't be put to
death for his crimes. Even the family of Hill's victim filed an
affidavit in June, recommending that Hill not be put to death. The
statement said the victim's family "feels strongly that persons with any
kind of significant mental disabilities should not be put to death.”
Hill
was serving a life sentence for the 1986 murder of his girlfriend when
his crime against Handspike, another inmate, took place.