There's also the argument that galactic conditions haven't been "right" for advanced civilizations until somewhat recently. Specifically that the metallicity o

There's also the argument that galactic conditions haven't been "right" for advanced civilizations until somewhat recently. Specifically that the metallicity of stars would need to exceed a minimum in order for civilizations to have the necessary building blocks for technology. It's hard to build a fusion reactor without the right elements. And it would be impractical to synthesize them in any practical amount. Especially since that would balloon your energy needs drastically.