"...Pardon me for butting in on an incipient flame war, but this is a very interesting, and essential question....
In my amateur opinion:
One who is delusional, and by definition can therefore be seen as mad by a majority of "rational humans", is not themselves a liar, since the deluded thoroughly believe what they say, believe themselves to be promoting the truth, and do not intend to deceive. However, their continuing promotion of untruths as truth, in opposition to a consensus present or future, put them at risk of being labeled as peddlers of lies.
Perhaps the veracity of the agent is independent of the statement, while the veracity of the statement speaks for itself. E.g. I may earnestly believe in the flatness of the earth; but if I teach it, in opposition to the consensus of many reasonable persons; I myself may not be a liar; but my information IS nevertheless falsehood presented as truth, and is therefore itself a lie.
However, history has shown many instances in which the consensus has been wrong, and also to be repellent of new reason. E.g. "The sun and other stars orbit the earth, as we all know, Sr. Gallileo; so kindly repeat your deductions again for the benefit of this inquisition."
So if a falsehood is believed by the majority, or is only believed by one individual, seems to have no bearing as to whether or not an assertion is false. Since teaching what is false as the truth has the same effect on the innocent as premeditated deceit, it is still lying, even though it is ignorant and not deliberate.
I suppose any scientific assertion must not only reconcile itself to all those that have gone before, but must also admit to and welcome the possibility of being overturned by future science in order to avoid lying.
Were physicists of 4th century Athens lying? Not when they were alive maybe, but in the hindsight of Newton, Faraday, Maxwell, Einstein, Bohr, Heisenberg et al they were!"