Hey, we're ALL nuts about space round here...
But a genuine nut case is someone who beleives in something that is manifestly not supported by evidence, and in discussions refuses to even comprehend the counter-arguments.
In all my time of being a "Mars-Nut" I was very careful to listen to my (scientific) opponents, engage them rationally, on their own ground and by their own rules. That was why some of them felt I was a little dangerous. I could not be ignored or refuted.
A TRUE nutcase raves on about irrelevant stuff, and ignores the counter arguments.
A scientist discusses the arguments and assesses the probability that he is wrong...