I agree that both of the statements you gave are not productive. "Interstellar travel isn't possible" rejects all theories past and future without considering their individual merits, which is awfully arrogant. "We have enough problems down here on Earth" is short-sighted, in terms of a geological timescale. In a billion years, our most pressing problem on Earth will be that the expanding Sun will kill all terrestrial life. Hopefully some forward-thinking individuals will have worked out space travel by then.
I only read the abstract, but I don't think the article is nearly as prohibitive as your statements. It says that diverting the radioactive hydrogen is a "daunting problem" i.e. hard but not impossible. Even if Near-C space travel _is_ invariably fatal, that's not so broad as "interstellar travel isn't possible". There's still wormholes and hyperspace and whatever exotic ideas we might come up with in the future.
"X isn't possible" statements have always held a special interest for me. To me it is that person stating that they, or possibly they think we, know everything there is to know about whatever the subject is they are describing. Many of the scientific advances from the past 100 years that we take for granted today were "impossible" 200 years ago.
As for the "enough problems here on Earth" statements, I always say that most likely the solutions to many of those problems will be solved directly, or indirectly, by visionaries chasing the dream of traveling to the stars. More than likely anyone who says they don't want to spend money on space exploration because of "problems" here is just saying they want to spend the money on their own preferred project, whether there's a benefit or not.
I only read the abstract, but I don't think the article is nearly as prohibitive as your statements. It says that diverting the radioactive hydrogen is a "daunting problem" i.e. hard but not impossible. Even if Near-C space travel _is_ invariably fatal, that's not so broad as "interstellar travel isn't possible". There's still wormholes and hyperspace and whatever exotic ideas we might come up with in the future.