Three possibilities I can see:
(1) Greenwald really can't think even one move ahead and see that he's just published a reason for any number of US adversaries to kill his source.
(2) Greenwald understands the implications of what he's published but is, owing to his own incentives, fine with the idea of his source being killed
(3) Greenwald doesn't believe what he's saying and isn't meant to be taken seriously.
Cards on the table: that guy could be reporting that water is wet and I'd still have him in bucket (3). Although now you kind of hope the freakshow government in North Korea is smart enough to bucket him the same way.