Okay I can see some people being okay with sitting back and watching Christian women getting their throats cut...
Why do you keep harping about Christian women, Cherry? Christian, Jew, Yazidi and Kurds make up maybe 10 percent of those murdered by ISIS. 90 percent of those murdered are
Muslim. Why don't you mention the vast majority of those killed by ISIS? Why only mention the religion of a relatively small minority?
It almost sounds like you don't think they count.

...what's harder to understand is how people can see innocent Americans getting butchered like sheep in San Bernadino by ISIS and not caring enough to do anything about it.
I can see several reasons for that.
First, Americans get butchered like sheep every day and we hardly do anything about it. How many people were butchered in San Bernadino
before those two ISIS supporters went on a rampage? How many since? How many Americans have been slaughtered since the San Bernadino massacre across the country by non-ISIS killers? What are we doing about that?
50 times the number of people are murdered every year, but because those two were "ISIS," we should invade another country and risk losing a few thousand more Americans to "keep us safe?" Considering the damage ISIS has done to us so far, it won't make a damn bit of difference.
Second, IIRC, those two murders were merely ISIS supporters. They were not directly supported by ISIS, did not follow any orders from ISIS, and basically did what they did on their own initiative. Destroying ISIS probably won't prevent such people from doing harm; they'll just find some other radical organization to follow. They didn't need ISIS to do what they did.
Furthermore, is that really the standard we want to use to go after organizations? That they "inspire" people to kill? How about those that inspired the terrorist Robert Dear, Jr? Shouldn't we go after them, too? Or those that inspired the terrorists Jerad and Amanda Miller? Shouldn't those bastards be stopped, too? Or those that inspired terrorist Timothy McVeigh? 168 American men, women and children dead, more than 680 injured. Why haven't we crushed those that inspired him?
It is because ISIS is "the other," while those other terrorists were inspired by people closer to home?

We are doing something about ISIS, just as we are doing something about the murders in our country and those that inspire them. But we aren't going to go overboard. We aren't going to break international law, have hundreds if not thousands of Americans killed taking and holding territory that we have no claim to, and justify everything that ISIS has been saying, just because they bloodied our noses. Because ultimately, amid all the terror and murder and atrocities that go on in this world, the ISIS cockroaches are a minor player. And while we will stamp them out, we will do so in a slow, sober manner that minimizes casualties (at least American) and hopefully does so in a lasting way. We won't let our outrage lead us into ill-conceived plans (like Trump proposes*) that will end up hurting us more than ISIS has done.
No, it ain't perfect. But if you've looked around, you've probably noticed that this isn't a perfect world. And it's hard to be outraged when there is so many other outrages going on all the time.