I personally don’t like the idea of an artificial “you don’t destroy/damage clothing when you repair it anymore” because it doesn’t make sense if the clothing you are repairing is really badly damaged, or if you are really stressed. You are dealing with the phreaking post apocalypse. Otherworldly nightmares could tear down the wall your hiding behind at any moment.
That’s something that will probably always be in the back of the mind of any survivor really.
Unless we want to say that positive moral may give a slight (read SMALL) boost in your chances of success, I don’t think it’s unreasonable that you will use more thread than necessary or that you might destroy a piece of armor that you where trying to re-enforce.
It adds tension, and encourages you to keep spares, or backups of your favorite equipment if you aren’t a nomad.