Greg Bear wrote an excellent pair of books based on this premise :

https://en.wikipedia.org/wiki/The_Forge_of_God

and

https://en.wikipedia.org/wiki/Anvil_of_Stars

Anvil of Stars is often said to be the weaker of the pair, but it haunted me for several reasons, not least the extremely spooky ending!

Cixin Liu’s Three Body Problem stories have exactly that premise.

In the books game theory means that the most prudent way to deal with a competitor species is to obliterate it immediately on discovery. The answer to Fermi’s Paradox is that everyone is keeping their heads down and and hoping no one notices them.

Humans, on the other hand, are merrily broadcasting away without a care in the universe...

Yeah, because living your entire existence in hiding, and instantly annihilating anyone else you come across just in case, is totally a worthwhile way to exist. Do you win if your civ makes it as far as the iron star era?

What do you mean by 'worthwhile'? And what would worthwhile be to an alien?

For all we know, the universe is jam packed full of Predator-like aliens who are the dominant species on their planet specifically because their society is built around dominating everything they can.

Well that is a fair point, we only have one example of a species capable of building civilizations to work from. It seems unlikely, however, that we are going to end up being particularly unique in that class.

I mean, if living before meeting aliens is worthwhile, then living with discovered and destroyed aliens should be fine, no?

Your point doesn’t really hold up if the effort to destroy a civ is basically zero, while the cost to defend is approximately unachievable.

Do you really even want to live in a universe like that? And if not, why contribute to creating it? Ultimately no one survives. There's no winning, you don't get a trophy for watching the last proton decay, so it is silly to survive for surviving's sake.

Plus, wouldn't it also attract the attention of the nice guy alien civs? They've been keeping their head down, just developing tech for more thousands of millenia - they probably care about civilizational diversity. The destruction oriented would surely be on the nice guy hit list for destroying all these nice diverse civilizations. So then it's just a question of whether a nice guy attitude would enable better wartech than a destruction oriented attitude.

I like being alive. I don’t generally extend my personal scale of experience beyond my neighborhood let alone intergalactic diplomatic relations. If we destroyed an alien civ, life would be as it were before meeting them, which was fine. Why do aliens need to factor into your world view?

Humans have managed to wipe out most of the interesting things on the planet without even trying

Yet we make an effort to preserve those things, and seek peace among ourselves despite our differences.