1: What is the point of a sham of a military trial that nobody is allowed into? Do you expect them to spill all their intel secrets for the entire world? The trial would be a sham. Why bother? Would it make you feel better if they said they held a 30 second trial on the battlefield before they executed him? because the "trial" he received would not be any better than that. It would be a secret trial, with only the top military people allowed in, with no information being released.
2: Manning is not a POW captured in battle.
3: We could have secured him, sure, but it still would have given the terrorists something to rally behind. As it stands now we followed Islamic law in dealing with Bin Laden. That's a far cry from holding him in some secret location, probably torturing him, giving him a top secret sham of a trial where he has absolutely no chance to win, and eventually announcing he was found guilty and given the death penalty.
4: The better question is, if they can throw the laws out the window when dealing with me, then why should they bend over backwards to treat Bin Laden with kid gloves? The whole reason we have the Patriot act is because of him.