And the reason of having tzaar because you’re not having tzaar is not considered valid by anyone who is not a brainwashed lubavicher.
It’s a Leshitascha. You (and DY, NCB) believe that the Frierdiker Rebbe wrote fiction. So the quote Beshem the Mitteler Rebbe (“How can one sleep in Makifin DeBina?”) was fiction. If it’s fiction, than any Tzaar we have from that quote is fictional, and fictional Tzaar doesn’t Patur you from the Sukkah. Although you haven’t sourced that fictional Tzaar doesn’t Patur you from a Sukkah either, btw. The only thing you said was that it was wrong for the Rabbeim to give us this Tzaar.
But Lubavitchers (and the Lubavitcher Rebbe) didn’t believe that the Frierdiker Rebbe’s writing fiction. So this quote was actually said by the Mitteler Rebbe, and there is an inyan not to sleep in a Sukkah if you:
1. Aren’t on a holy enough level to be in control of yourself in your sleep and,
2. You realize the holiness of a Sukkah.
So according to us, it’s quite a reasonable psychological tzaar (The Sukkah itself makes us feeling guilty when we sleep there). And I’m still waiting for a source that psychological Tzaar doesn’t count.