If a man wants to engage in such crackpot pseudo-academic pursuits such as proving that Sir Francis Bacon was the true author of William Shakespeare's works, or that the earth is a flat disc round which the sun revolves, we should let him and his nonsense fall of its own weight.
We should not make the propagation of his ideas criminal offences, for to do so would be to give them a credence in the eyes of credulous observers that they do not deserve. How often have we heard the claim that if someone's upsetting the powers that be, they must be on the right track?
Jailing the likes of David Irving merely plays into the hands of the anti-Semitic nutters in the Middle East and elsewhere.
Holocaust denial would be far less attractive if its proponents were treated like the delusional eccentrics that Baconians, flat earth geocentrists, and other similar amateur kooks are. Ignore them, or if you must pay attention to them, laugh them off the stage.
Malignant as they are, they thrive on fear; they will perish under ridicule.