Having been on crime boards for years, I have to say it does go on here; we just don't always hear the gory details, nor would we want to. The worst of course, are ones with children, and the elderly. I'll never be able to fathom how anyone could do such horrendous things to anyone else, let alone those who are defenseless or trusting.
I do think we should be aware of what can happen, if only to be somewhat better prepared for what might come close to us and our own families.
I also think some of the things you've discussed could happen here in the not so distant future, as we get more and more involved in what happens in other countries; we have terrorist cells here already, and our borders are open to just about anyone who wants to come across. The drugs coming across are bad, but not the worst things coming into this country. I can really understand why the "preppers" are doing what they are doing - I just don't see how we can be prepared for any possible scenario.
Seems like it's just 'one day at a time', and hope for the best, but don't be surprised if it gets worse. Sorry if that sounds too negative, but that's how I see it now.