One does not need immunity for legal orders. You are deeply, obviously incorrect in your views and clearly ignoring the context and content of the decision. Under this decision, the President has total immunity for the exercise of his Article II powers, which include being the Commander-in-Chief; as such, he can order the military to do whatever he wants, and cannot even be investigated for it. Were he to order the military to arrest and execute someone, then pardon those that followed his orders, there could be no civil or criminal penalties.

I’ll leave some excerpts from the decision below, for your amusement. And I won’t be responding to you further. Please, enjoy.

From the decision:

Under our constitutional structure of separated powers, the nature of Presidential power entitles a former President to absolute immunity from criminal prosecution for actions within his conclusive and preclusive constitutional authority. … At least with respect to the President’s exercise of his core constitutional powers, this immunity must be absolute. … When the President exercises such authority, Congress cannot act on, and courts cannot examine, the President’s actions. It follows that an Act of Congress—either a specific one targeted at the President or a generally applicable one—may not criminalize the President’s actions within his exclusive constitutional power. Neither may the courts adjudicate a criminal prosecution that examines such Presidential actions. The Court thus concludes that the President is absolutely immune from criminal prosecution for conduct within his exclusive sphere of constitutional authority. … At a minimum, the President must be immune from prosecution for an official act unless the Government can show that applying a criminal prohibition to that act would pose no “dangers of intrusion on the authority and functions of the Executive Branch.” … In dividing official from unofficial conduct, courts may not inquire into the President’s motives. Such a “highly intrusive” inquiry would risk exposing even the most obvious instances of official conduct to judicial examination on the mere allegation of improper purpose. Nor may courts deem an action unofficial merely because it allegedly violates a generally applicable law. Otherwise, Presidents would be subject to trial on “every allegation that an action was unlawful,” depriving immunity of its intended effect. … But under our system of separated powers, the President may not be prosecuted for exercising his core constitutional powers, and he is entitled to at least presumptive immunity from prosecution for his official acts.