Your personal opinion of what constitutes bravery or cowardice is, frankly, worthless.
There are two considerations here:
(1) Life without parole is a reversible penalty if legal mistakes have been made.
(2) Placing the power of life or death in the hands of the state is a weighty matter.
In the United States of America, for the moment, this power may be exercised responsibly and justly. In much of the world it is not. And the Church has the responsibility to weigh matters universally, not geographically or temporally.