It may be worth the risk but that doesn't change the fact that what you refer to as "Chicken Littles" represent power players in an intractable political dynamic. The only way this kind of cooperation happens is when humans move past current notions of nation states and begin to think strategically as a species.

Not if an independent organization (think a Corp, not a gov) is the party responsable. They would have no incentive to do such a thing, in fact they would have a negative incentive.

Too bad nuclear tech is basically too regulated for any non governmental organization to experiment inexpensively, not to mention the other nontechnical issues.

On a side note, this is why Independence Day and other interstellar alien invasion movies don't make much sense. The amount of resources necessary to move between solar systems in an even slightly reasonable timeframe is orders of magnitude larger than what you need to obliterate all life on the planet in just a few seconds. The idea that you could meaningfully fight back against an interstellar traveler is silly.