Is the crackpot being responsive to the issues and giving arguments – arguments are what matter, not people – or is he saying non-sequiturs and refusing to address questions? If he speaks to the issues we can settle it quickly; if not, he isn't participating and doesn't matter. If we disagree about the nature of what's taking place, it can be clarified, and I can make a judgement which is open to Paths Forward. You seem to wish to avoid the burden of this judgement by hedging with a "probably".

Fallibility isn't an amount. Correct arguments are decisive or not; confusion about this is commonly due to vagueness of problem and context (which are not matters of probability and cannot be accurately summed up that way). See https://yesornophilosophy.com