Is South Africa safe? Like any place in the world, it depends on where you, the time of day (or night), how you're dressed, how you act, etc. There are many places in the US which are more dangerous than many places in South Africa.
I've been to virtually every province of South Africa, mostly in rural areas, but a few cities and towns as well. I have a number of friends there as well. I have never felt particularly unsafe, and they've told me they don't feel particularly unsafe. This doesn't mean that there aren't people who would target farmers in rural areas, but I don't think the facts bear out that white farmers live in fear of their lives.
Now, if I was a farmer in South Africa and the US offered permanent residency to me and my family, help with resettlement, etc., would I take it up? Probably, but for economic reasons, not for reasons of safety.