"It is not the critic who counts; not the man who points out how the strong man stumbles, or where the doer of deeds could have done them better. The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood; who strives valiantly; who errs, who comes short again and again, because there is no effort without error and shortcoming; but who does actually strive to do the deeds; who knows great enthusiasms, the great devotions; who spends himself in a worthy cause; who at the best knows in the end the triumph of high achievement, and who at the worst, if he fails, at least fails while daring greatly, so that his place shall never be with those cold and timid souls who neither know victory nor defeat." - Theodore Roosevelt

It is all very well to quote Roosevelt and yes he is correct. But there is a difference between putting in the hard work and trying achieve something great, SpaceX have done that and will continue to do great things, and the difference between claiming a million people on Mars.

The thing is there are many folks out there that were the nay-sayers and were completely wrong but also many that were completely correct. They are typically not remembered. It is one thing to make bold claims, it is another to out right deny the realities of the universe because they get in the way of a vision.