Actual torture is a punishment, not an information gathering technique. As an interrogation technique, torture is completely fucking useless at gaining actual information.
You're getting it wrong. Torture is fucking useless at getting a (truthful) confession, not at gathering information. Because with enough torture, a person will admit to anything even if they didn't do it, just to make it stop (and you won't stop until you've heard exactly what you want).
I'm assuming you mixed those up, and meant it's *not* useless at getting a confession, and is useless at gathering information?
The only justification to torturing without even asking for anything is if you're Darth Vader.
You don't seem to understand the power scaring everyone shitless over what you might do if they cross you carries. That's a big part of how organized crime works.
Really, anything done to him is a lose/lose situation. Make an example of him to deter others from being as fucking stupid as he was, and you just make him a martyr and encourage more idiocy. Let him off easy and you send a message that such behavior is acceptable.
But depending on who you ask, such behavior IS acceptable.
If you're a government that treads over people's rights, you may think it's not. A lot of people would however think the government's actions are the ones that aren't acceptable.
Ok, even ignoring the question of whether or not someone doing what you're claiming he did (expose some intangible "wrongdoing" or somesuch) would be doing the right thing (probably not, but moving on),
Manning did not do that. He stole random documents containing only the most trivial of information proving that
GASP US intelligence is actually doing what intelligence agencies
fucking do, and that diplomacy
GASP AGAIN entails
more than fucking press releases. None of which had a flying fuck to do with his grievances against the military (a completely separate entity from the state department), which were comprised of trivial, isolated incidents being mishandled by his (low-ranking) direct superiors. Manning did something extremely fucking stupid for extremely petty and misguided reasons. Assange, loathsome jackass though he is, handled his end quite well, if for even more fucktarded reasons ("I'ma piss off dem fascists into bein more fascisty so GLORIOUS ANARCHIST REVOLUTION AGAINST THE OPPRESSOR!"
).