Dear Un-follower (if you read this)
I had a feeling this might happen, and I'm sorry to see you go, but we obviously disagreed about something about which I feel very strongly. Maybe I was too fierce - maybe you were, too - but nonetheless, I'm sorry to see you go. Thank you for following me, and for all your comments. This is the risk we all take when writing about things near to our hearts; people won't always agree. But, dear late follower, I wish you had done your research, as I have. Then we need never have fallen out at all.
Best wishes, and no hard feelings, eh?