is that we both overestimate and underestimate them.

They pose VERY little threat to our well-being in the west. They have very little chance of winning any wars against western military either.

BUT

They do pose a threat in destabilized countries that the West has no patience for/interest in...

the West has proven and continues to prove that it genuinely doesn't care about people for altruistic reasons... ISIS - and many revolutionary terrorists groups give people a sense that either they are cared about personally OR that by joining they can take back control from an uncaring elite...

Look at what's going on in Yemen now... why wouldn't a Yemini who is watching his family starve to death at the hands of the West and Saudi Arabia NOT want to fight or punish their oppressors...?

But in the West we mostly are kept in the dark about these sorts of crimes, and so are befuddled by the allure of ISIS, etc.

Until we address our foreign policy, we can't ever hope to stop ISIS and other ISIS like groups.