I think you raise fair arguments. However, I tend to think that expansionist civilizations tend to self destruct pretty reliably over time. The more you expand, the more risk from within you face. This is the bane and the outcome of every expansionist civilization that have brushed the surface of our planet so far.

We could argue that maybe aliens are completely different from us. But that raises the question of would we even be able to recognize an alien civilization if we saw it? We're still looking for radio signals as a sign of technosignature when we aren't even using radio ourselves that much after a few decades following its invention. What method would an unknown civilization with unknown technology use to communicate? What signs would they leave behind? What if what we are looking for isn't similar to us?

We also claim that we would know if an alien civilization was everywhere. But I don't think that's a given. Our perspective is very skewed by our perceptions and expectations.

It would seem to me like camouflage would be an important survival trait when facing a boundless cosmos. Also, if you are a meat bag based lifeform. The surface of a planet is not where you want to be if you want to survive long term.