I see this topic pop up in various forms throughout the site, but I'd like to begin a pure and dedicated discussion of "The place for grand conspiracies as applied to debate technique." "Grand" means those that are alleged to be affecting all of humankind in general. Not just RE, but most certainly including it.
This post is intended as a reference list, so I will be editing it occasionally for updates and completeness.
All the "grand" conspiracies share one defining characteristic that sets them apart from less controversial ones; saturation of influence. Because of their scope, literally anyone can be part of it, allowing any contradicting evidence to be dismissed by the theorist as part of the conspiracy, creating an endless cycle of self support. I've coined the term "The Talisman of the Grand Conspiracy" (the TGC) to reference this concept when used as an indisputable argument in debate.
1. Scientific debate requires that all claims be testable in a single way acceptable to both sides. Since the TGC cannot be tested in this way, it is not scientific; ergo, invalid in any scientific debate.
2. To "believe" only requires acceptance, which can be based on science or not.
IF 1 AND 2, THEN...
3. Using the TGC refers to a belief system not based in science regardless of what the user may say about the root of their belief.
This tells us that there is nothing inherently wrong with using the TGC. The rub is when a theorist claims to be willing to participate in a scientific debate, while insisting on using the TGC. They are mutually exclusive and cannot be claimed together.
Some debaters actually prefer to disrupt any meaningful scientific debate by injecting unscientific statements rather than restrict their arguments to the testability criteria. Doing so suggests that one does not have any other argument and can even cause others to doubt one's veracity from that point forward. For this disruptive type of debater, the ultimate goal is to derail any meaningful exchange, so essentially they've won.
It is this reason we must take great care to always keep the debate scientific and ignore the rest. For this forum, the TGC (Talisman of the Grand Conspiracy) is nothing short of the third rail. Step on it and the debate is dead on the spot.