I have a friend, a retired reference librarian, who asked me to locate a line–maybe it’s from “The Death of King Arthur,” maybe not:
“Lest one good [thing] corrupt the world.”
Does anyone among the Teeming Millions know where this line came from? Thanks very much. 
Could it be this, from Alfred, Lord Tennyson’s The Passing of Arthur-
“And slowly answer’d Arthur from the barge:
The old order changeth, yielding place to new; And God fulfills himself in many ways, Lest one good custom should corrupt the world.”
It’s “The Passing of Arthur,” from Tennyson’s IDYLLS OF THE KING, and it goes thus:
And slowly answer’d Arthur from the barge:
The old order changeth, yielding place to new;
And God fulfills himself in many ways,
Lest one good custom should corrupt the world.
Uke
DAMN it. That’s the last time I try to answer first.
Thanks, guys.