[stcredzero]

How does it increase our knowledge, or ability to do new exciting things, or our ability to "push the envelope"?

It keeps resources from being wasted that would otherwise actually contribute to our ability to "push the envelope."

It doesn't. It's a waste of time and effort.

When something which really is impossible or impractical is called out, then huge amounts of resources can be redirected to genuinely beneficial projects.

https://www.youtube.com/watch?v=obS6TUVSZds

Are you advocating that we never doubt? Should we just "listen and believe" and somehow our positive energy will make things happen? Sorry, no. Scientific analysis has predictive power. That's what Elon Musk is all about.