Everyone, including the president, is allowed to express their opinion. No one, including the military, can be indemnified against critical opinions. Oh, and I don’t think people have to apologize for their opinions, particularly if those opinions don’t cause measureable harm.
On the other hand, presidential opinions that result in the death of thousands of our soldiers and tens of thousands of civilians, are opinions that I think cross the line.
You can conjure up a lot of moral outrage about things that happen, but it is very disingenuous to make big noise about small matters and concoct phony rationale about earth shaking blunders. My advice is to pick your moral causes carefully, they define your character.