[postalrat]

In the books the weapons to destroy entire star systems can be used seemingly without to much cost.

[Aeolun]

I think that’s more because any cost is acceptable if you are talking about the continuance of your civilization.

We could spend a million years building a single civilization destroying weapon, and it would still be worth it.

Since we’re not likely to encounter another civilization much more often.

Of course, humans couldn’t really stay interested in something that long, so the practical range is probably a few decades :P