Ask anyone at NASA where they intend to build a ship to Mars... IN SPACE.:
Intentions are wonderful things.
When they get around to actually building one, get in touch with me - there might be something more persuasive to the argument then.
Europeans spent hundreds of years "intending" to fly by designing and building contraptions that in many cases included the very important concept of flapping wings. 'Cause, you know, if that wasn't essential then birds wouldn't all flap their wings.

In any event, as far as I'm concerned building the Enterprise on Earth is justified entirely by the shot of Kirk looking up at it under construction. "Star Trek" has always played so fast and loose with science and plausibility in the pursuit of storytelling that nothing in its history requires giving up a moment like that in order to somehow be "true to reality."