Let me know if I'm summarizing this fairly:
Your concern with people open-carrying at ICE protests is that it risks creating a situation where Trump can declare Martial Law. If that happens, he could use bombs against civilians, with no way for the courts to tell him to stop.
You agree that there is nothing stopping him from using tanks and bombs on civilians right now, but if he does, the courts will tell him to stop at some point in the future. And he probably would, but then he would come back later, probably with more weaponry.