Well, Calley was Nixon’s pardon, and Nixon isn’t in office anymore.
That pardon was wrong, but on the other side of the issue a lot of the people calling for Calley’s head were just the pot calling the kettle black. And Captain Medina was completely railroaded - even a famous liberal lawyer was willing to step in to defend him.
There’s really no similiarity between the cases. A pardon can only come after a conviction and after the appeals process has run its course. We’re not even close to any convictions in the Haditha case.
BTW, the pardon for Calley was issued during Ford’s presidency, not Nixon’s. The process takes a long time. If there are any convictions for Haditha, the next president will be the who could grant a pardon.