If we can shoot 'em, we can hold 'em?

Did I hear Justice Scalia embrace the following proposition during oral argument before the Court today?:

If the executive branch can shoot enemy combatants, it can detain them (as long as it wants and in any fashion it deems fit).

Justice Scalia and I went to different law schools -- or we got a different legal education. I was taught that the following sort of argument is not a valid syllogism:

The government can do X; therefore, it can do Y.

Stated less formally: The considerations that suggest that the military should be able to kill enemy combatants on the battlefield do not necessarily demonstrate that the government should be able to detain alleged combatants indefinitely or under any circumstances.

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I think I also heard Justice Scalia suggest that the President could take any steps that he deems necessary and proper during this time of war(s).

Question 1: If so, could the President abolish the Roman Catholic Church in the U.S. -- if he thought that doing so would promote the conduct of the war(s)?

1A. If so, would Justice Scalia resign?

Question 2:Could the President seize steel mills (or computer companies) if the President thought that doing so is necessary for successful prosecution of the war(s)?

More questions: Mosques in Detroit? Harvard Law School? The Supreme Court? (A wag might suggest that successive Presidents -- liberal and consrevative -- have largely accomplished the last objective.)