I didn't realize your blog was about unchurched people of faith. I will be following you.
I've encountered substantive spiritual evil three, or possibly four or five, times in my life, each time too stupid or unaware to realize what was going on. On the last occasion, I was being pretty heavily influenced without realizing it; and suddenly, abruptly, the influence vanished, and a voice spoke in my mind identifying what it had been. The most important lesson I learned from this was not that evil was real, but that Someone cared enough to intervene on my behalf despite my wandering off the path.
I made an abrupt change in my life that night. And when I looked back it taught me a few things about spiritual evil. One is, it's smarter than you are, or, at least, it can cloud your thinking to the point where smart doesn't matter.
I've been off the reservation for more than 30 years. Naturally, I still believe in Jesus; but I also believe things that would keep me out of most churches, if I were honest (which I would have to be). And then, there's the old thing about being a stumbling block -- which I definitely would be, just being me.
I've been walking this path alone -- at least as far as other people are concerned -- for a very long time. Perhaps that's why God has been so gracious with me. It doesn't keep me from worrying, though.