I'm not having much luck encouraging people to avoid inflammatory characterizations, which includes characterizing something as a lie or a person as a liar. To show something or someone incorrect only requires providing the evidence. To show something a lie or someone a liar requires information that is usually unavailable. Here at EvC Forum I encourage people to assume someone sincerely believes what they're saying unless there is clear evidence to the contrary.
This word is generally proscribed when refering to another poster on this forum, but I don't think this means we can't say that, for instance, Clinton lied about his relationship with "that woman." This is an accepted fact.
What exactly is a lie, and what are the boundaries of protocol to use on this forum: why is "lie" worse than "falsehood"?
The difference seems to center around the intent to deceive.
To deceive is to convince someone of a falsehood. There is little doubt in my mind that people like Ken Ham and Don Batten try to convince people of something that is false. I believe that it can also be shown in some cases that they must know it is false (see Dendrochronolgy Fact and Creationist Fraud).
Ken Ham's "museum" is certainly designed and built with the intention to convince people that the world is 6000 years old and that there was a world wide flood. Both of these are known falsehoods on the level of Clinton's lie.
In Don Batten's case he makes two contradictory claims (among other intentional misrepresentations): (1) that you cannot determine false rings with the science of dendrochronology and (2) that he found "up to five rings per year can be produced" in a particular species. One or the other of these must be a lie, as he cannot "sincerely believe" both at the same time.
Falsehood, deceit, intention. QED?
While I agree that calling other participants liars is not conducive to good debate, I see no problem with detailing the lies of people not so protected.