[api]

I tend to take "it's impossible" statements from scientists seriously only when the reasoning can be firmly tied to an extremely well established physical law with no "wiggle room."

For example I accept that faster than light travel and inertialess propulsion are both impossible. If either of these things were shown to be possible, it would mean that there are huge errors or oversights in the most well established areas of physics.

I also accept the conditional impossibility of things that are just provably beyond our current ability for fundamental reasons, like a Dyson sphere. I don't know of any physics that says you could not build one, but for us it'd be like dust mites building the international space station.

For everything else I leave the door open. People have historically underestimated creativity.

For the first types of things, taking preparatory steps would be irrational. We don't need to plan for the arrival of FTL travel because we have no reason to think it will ever arrive.

For the latter types of things, preparing does make some sense as long as it's not unreasonably expensive. We do have reason to believe that a large quantum computer might be possible, so mucking around with a bit of code to defend our security against a surprise seems rational.