And if you parse the sentence correctly it makes perfect sense. “That is a stain” modifies “long and sordid history” which any non-troll would get immediately.
BAZINGA!
The phrase that precedes the word “that” reads like the subject, not a modifier. The sentence may diagram either way but it sounds really really awkward when read out loud from a common sense point of view. Legalese is not for everyone - especially the common sense crowd. The casual observer would see this instantly - if they looked.