[qw]

What if FTL is not possible? In that case the attack will take a long time to reach us, and in the meantime we will be much more advanced technologically and could potentially defend ourselves.

In sci-fi we see warp drives, worm hole travel, phasers, photon torpedos and energy shields around ships. But what if none of that is possible? In that case, we might even have the technology to defend ourselves today if we manage to detect the attack in time.

It's a huge risk for a civilization to attack us. Even if they have capabilities that are beyond our technology, there might still be limitations based on the laws of physics. And if they attack us, they risk a response.