Good writer, but apparently a horror of a “parent.”
I read “The Mists of Avalon” a long time ago, and while it was well-written, some things smelled kind of “off” to me, but it took this information coming out to snap the last pieces of the puzzle into place.
And the problem wasn’t restricted to this couple either. It’s been an issue in sci-fi fandom for a while. Here is a document, rather lengthy but comprehensive on the issue:
WARNING: Some of this could be very difficult to read, on account of the unsparing nature of the material.
If your stomach is still holding up well after that, look up “Breendoggle”, and you will find 60’s-era ‘zines that show that Walter Breen’s tendencies were already well-known in southern California fandom at that time.