Astronomy

Suggesting that we move towards space-based astronomy doesn't mean he's out of his mind. He might not be a professional astronomer or astrophysicist, but that hardly indicates insanity.

They had an opinion and expressed it. You can then reply and explain why you disagree. No need to call them insane for expressing their thoughts.

Considering their instance, I'd assume they're more out of their mind than huffing Elmo.

Another important part in this argumentation is that each type of telescope has its use case:
Extraterrestrial telescopes, as they are not objected by atmospheric blur can obtain much better 'images' from the cosmos even of weak, low brightness signals, which makes them best for observing the 'far' cosmos until the boundaries of recognition.
Yet, they are and always will be much more expensive and more difficult to maintain than terrestrial telescopes. Thus, using them for observing our cosmic front yard, the milky way, is like shooting with canons at sparrows.
Due to their cost, extraterrestrial telescopes also will always be 'few', too few to effectively keep track of the objects around us. Thus, 'cheap' terrestrial telescopes, large professional ones and small ones run by amateurs, will always be needed to observe the objects 'closely' around us, i.e. in our galaxis.