We have a separate apartment too and I can't imagine a situation where I wouldn't feel 'safe'. I suppose that the only problem would be if guests were doing something illegal enough for me to call the cops.
I would never dream of checking out guests and I use IB.
I'll probably get lots of people disagreeing with me and I've rattled on about this here before, but when I had a traditional B & B there was no way to check out guests. There was no internet and certainly no social media in those days. And these were guests who were staying under my own roof.
And during those years, I never had a troublesome guest. During my time with Airbnb (to date) there has only been one group of guests that I had to ask to leave.
So I guess that what I'm saying is that as an 'old-timer' I think that today's Airbnb hosts are very lucky in that they can read a potential guest's reviews, check them out on social media, ask a ton of questions and have a decline button!