It does seem the US and many of its citizens are okay with this happening in another country. But if it where to happen in America does anybody think it'd be okay?
For 'this' to happen quite a lot of other things would need to happen as well:
-America would have a second Civil War
-The New Confederates would take over a large part of the country, killing or expelling all federal government officials
-In this New Confederacy slavery would be reintroduced, women would be forced to dress modestly, music would be banned and non-Christians massacred
-What was left of the US government would be unable to retake the lost states
-From the New Confederacy terror attacks would be launched against other countries
Now we'd be in a similar situation. Say a country like Brazil is being attacked from these rebel held territories and with the permission of the US government launches a drone attack a town in Mississippi where terrorists are gathering.
And they hit a US civilian who traveled out of his own free will to the New Confederacy.