That's where the problem is--telling people they are inferior. If someone is bullied for being short, the answer isn't to say height is constructed. The answer is to stop bullying.

Technically, a fair bit of human diversity is actually indistinguishable from being defective for any reasonable definition of "defective" (which acknowledges that there is at least an implicit goal, and that this one has a rare difference that makes it less suited for achieving that goal). But because human society enables a massive diversity of purposes, the answer there is simple. If you have kitchen scissors with a defective herb stripper don't use it as a herb stripper. Just use the scissor function. They might be your best kitchen scissors otherwise--don't demand complete perfection, take advantage of what tools (and people) can do, not what they can't.

If I have a defective immune system, I probably shouldn't work in health care and that should be okay--I shouldn't be bullied for it, but if I am, we shouldn't say "the functioning of the immune system is constructed".

If society insists on binary, that's wrong. If it's binary* (* this is biology, there are always exceptions), that should be okay. We can tall it something else (e.g. "bimodal"), but we shouldn't lie to be nice. We should just be nice.