That is indeed a nightmare scenario, in no small part because of the “draw us into” aspect, which of course could be avoided if we didn’t have delusions about both the threat to the US and our ability to do anything about it. But it is not more likely than three dozen other nightmare scenarios. The world is full of nightmares. We focus on some, and not others, less out of rational calculation and more out of biases.
More likely than not we’ll lose more Americans in bathroom accidents over the next five years than we do to ISIS. And that’s a pretty fucking marginal cause of death.
That doesn’t make them not a big problem–mostly for the many Muslims of the region. It’s just a bit bonkers to think they are a serious national security threat to the United States of America. As a humanitarian threat, sure. Potential economic threat, maybe. But not in the top ten on either count.