NASA doesn't have the same objectives than Musk regarding mars. And I did not call Musk an idiot.
Look, I understand people can have dreams that I neither understand nor approve. As you correctly pointed out, as long as they don't divert tax payer money to fund them, I'm more or less fine with it.
Yet, when I see someone doing something that I consider silly, or even suicidal (for mars the term is almost appropriate), I feel compelled to at least say it loud. Like if I saw Franz Reichelt just before he jumped from the Eiffel tower[1]. I would say "don't do that, you'll kill yourself" and nobody should blame me for saying that. Well, in the case of the colonization of mars, to me that sounds like a terribly wasteful and dangerous idea, and I feel compelled to say it whenever the subject comes up.