I just finished this, and... holy shit.
It appears that "John Konrad," or whoever the end guy was, appears to have only been in Walker's head, because once you get to the penthouse, Walker ends up hallucinating a bunch, and the guy outside the elevator says, "what are our orders?" I'm still confused on who that voice was supposed to actually be. Was it actually just a hallucination? I can't recall if any of your squad acknowledged Konrad talking, or if they only knew what was going on by what Walker told them.
EDIT: I just saw the epilogue, where soldiers come to get you, and there was a decision to either open fire on them, or drop your gun. I dropped my gun. The game is constantly giving you an out to kill yourself, or do something that gets you killed.
There are no heroes.