He's a deranged mentalist because he either:

a) is telling utterly unbelievable lies to avoid standing trial for a murder he committed and is therefore a deranged mentalist

b) is telling the truth - that he was effectively spying on Hezbollah, drugs cartels and corrupt government officials in South America whilst living in the jungle next to them, in which case he's a deranged mentalist with a death wish.

Basically it looks like we're getting to the truth of the matter which is that John McAfee is someone who believes he is above the law - either because he kills people and thinks that he shouldn't be prosecuted for it, or because he hacks into local government official's computers, uses blackmail and honey traps to get what he wants and effectively acts as a one-man hostile inteliegence agency against his own country and thinks that's acceptable.

Either way, the safest thing for society is to put him behind bars.