Fair enough, and I alluded to that with my EM-Drive comment. But that brings up the "leapfrog" problem: "popsicles" might wake up after 20 years en route only to be greeted at their destination by people who arrived five years earlier with the newly-discovered "magic carpet" propulsion system. And as TFA points out, by the time we even get close to thinking about such decisions, our robotic exploration tech will have advanced to the point where sending humans out there for pure science would be a needless waste of resources.
Relativistic travel is an interesting issue, especially for travel within the solar system. For example, let's say you're traveling from Earth to the Kuiper Belt, a distance of roughly four or five light-hours, and you make the trip at 2% of C (including acceleration and deceleration at either end), giving you a (subjective) trip time of a few months. How much 'objective' time would have passed back home? A year maybe? That would probably be acceptable to most people, especially if you could still send messages back and forth along the way. (It would be weird to watch weeks go by in days, but I reckon folks could adjust to that.)
Ultimately, we're not arguing against each other here. I acknowledge the fact that technological advances will (most likely) extend our reach exponentially in the coming decades. But I still think TFA is largely correct in framing the next century or so squarely in the Earth-Mars neighborhood.