> I wish there was a good way to transfer these highlights from my Kindle into Anki flashcards automatically

Wouldn't the result be actually opposite from anticipated? It's exactly writing about the stuff by yourself a way for remembering it. It won't stick if you just automate the process. Or rather it will, for long enough to deceive you into thinking you know it, but you'd probably forget it after a while anyway. Writing anything by yourself, or ideally handwriting, makes it stick. At least it works for me. I spoke with some friends of mine and this system seems to work for them, either.