And if on that basis one wanted to say, "We won't colonize even to Mars in the next hundred years", I'd nod along and accept that as a reasonable conclusion.
But if you think it's reasonable to say "never beyond Mars" based on that reasoning, you're a fucking idiot. Nobody could predict 2015 from 1015 (much less from, say, when the pyramids were being built); anyone who thinks he can predict 3015 (much less 5015) from 2015 is the sort that should be immediately dismissed as a fool.
Screw adventurousness or industry; it's just about the folly of drawing absolute conclusions from vastly insufficient data. We don't have physics for, literally, 95% of the universe (you know, all that "dark matter" and "dark energy"), and we certainly don't have any "psychohistory" that can predict human culture a thousand years ahead even if we posit no breakthroughs in physics at all and assume that there will be no genetic engineering that changes basic human psychology.
If you're predicting humanity will be wiped out by global warming or rogue AI or something before we colonize Mars, that's one thing. But "Getting beyond Mars (with humans) is impossible . . . culturally forever" is too stupid for goddamn words.