This guy is a complete and total moron.
ISIS is not just in Syria, they are all over the MENA and Southwest Asia. Besides that, their ideology is deeply embedded within Islam, which almost 25% of the entire world’s population hold as their religion (not so of Nazis or Japan who had relatively small populations).
You kill today’s ISIS (or the many sub groups of terrorists) there will be a new crop of them tomorrow even more determined than before. They can make new terrorists faster than we can kill them.
This is not the same as WWII. There are no standing armies. On top of that, the ideology behind ISIS is widespread. Even people who don’t like ISIS or ISIS-like groups do support a caliphate of one sort or another and for their sect to be the superior sect over the others.
You are wrong there. You just gotta have the 'want to".