Unfalsifiable

Conspiracy theories are designed to be unfalsifiable: every criticism can be dismissed as "whitewashing by the conspirers", and every concerns can be summarized as "part of the greater conspiracy".

Popper introduced the so-called ‘demarcation problem’ of identifying what distinguishes pseudoscience from science. Popper's suggestion, as I explain below, is that, unlike real science, pseudoscience is unfalsifiable.

Unfalsifiability: The main problem with any particular conspiracy theory is not that it's wrong, but that it's inarguable; not that it's false, but that it is unfalsifiable.