Because that would have the opposite of the intended effect vis a vis stopping future leaks of classified material.
How so? This just so happens to be the perfect storm of a U.S. service member who was willing to sell out his country meeting another person who is all to happy to diseminate said information to everyone in the world. I think a bullet would go a very long way in plugging potential future leaks. And just to show I dont discriminate, the soldier should get one too.
You don't think the assassination bit is a little extreme?
Also, I'm sure the Soldier will get what's coming to him.
EDIT: not a bullet