What Manning did has no relevance on how he is currently--that is, prior to his trial--being treated. By that I mean Manning's crimes do not make it okay to punish him without a trial. Punishment before trial is not justice; in fact, it's injustice, contrary to the entire point of having trials in the first place.

It is very much in the US's interests to publicly torture Manning. It sends a very clear message: Manning is a soldier, and soldiers are pretty highly regarded by most of the US. The message is, if we're willing to do this to a soldier, imagine what we'll do to you--"you" being anyone, soldier, civilian, or foreign national, who wants to try to leak sensitive material.

The idea that Manning is being held under prevention of injury protocols solely for his own safety (even recognizing that ensuring his safety is necessary to bring him to trial) is naivete at best and willful ignorance at worst. We have a pretty poor track record when it comes to the rights of people we decide are enemies. If it looks like we're acting heinously when we deal with an enemy, it's probably because we're acting heinously.

If you want to see Manning tried and shot, well, okay--let's do that. Personally, I'm not sure the death penalty is warranted in this case, but that's a different argument; at the very least, shooting him after trying him for treason would be the proper execution (no pun intended) of justice as this nation subscribes to the concept. But to hold Manning under his current conditions and claim it's justice is to be either appallingly unaware of political reality or appalling unwilling to accept those realities.