Then don't arrest them, just deport them.
Legally speaking, you are correct.
Now imagine a group of foreign Japanese students at an American state college in January 1942 laughing about Pearl Harbor, and regretting that the carriers were missed.
Do you think it would have been a legal matter, or a bare knuckles matter?
Of course, the Japanese were at least in marked airplanes attacking military targets, not cutting stewardesses throats to fly planes into buildings full of civilians. After enjoying American open door hospitality.
Forget bare knuckles: these Saudi students deserve baseball bat massage therapy.