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.