For what it's worth, the situation isn't really that we've established that it isn't clear flossing helps, it's that we haven't established with the kind of evidence HHS requires that flossing helps. Those sorts of studies are hard to do reliably with things like flossing.
Do you think the evidence we do have, which doesn't rise to the level required by the HHS, is in fact strong enough and that we should rely on it?
The quote doesn't sound encouraging:
Overall there is weak, very unreliable evidence which suggests that flossing plus toothbrushing may be associated with a small reduction in plaque at 1 or 3 months.
Rationality quotes are self-explanatory. Irrationality quotes often need some context and explication, so they would break the flow in Rationality Quotes.