I've always considered the phrase "international law" to be code word for "hate America first." But, to the point, he is correct. "International law" does not truly exist and is totally useless to combat terrorism. The terrorists will ultimately win the terrorism war by simple means of attrition, because they are in unlimited supply. It's time to limit the supply.
Starting with the mosques. (Saudia Arabia first.)
I believe terrorists are in very limited supply. You make it seem as if just anybody can and will become terrorists. That doesn't ring true to me.
I would argue that a terrorists stands in a similar position as a pirate did in the 1600s. Any government could strike at them, kill them, drag them off, try them, and hang them without the nation where they happened to be located in or operating out of objecting. IMHUO.
But, keep your powder dry.