“Any organism that evolved to intelligence would have to be fairly aggressive, both to obtain the scarce resources needed to develop and power a brain, and to be able to defend itself. Because there is only so many non-technological entities a planet can support before Malthusian situations will arise.”
Well, that’s how it seems to have happened here. But aren’t we then extrapolating from an example of one?
Freegards
Organisms have to feed. Energy to live must come from somewhere. That would be other organisms, unless you're a plant.
Perhaps there is a race of intelligent beings, somewhere, that feed directly off of sunlight. They're peaceful, benign, and have to reproduce, unless they're immortals, if the race is to continue to exist. If immortal, maybe they're angels; and they probably didn't evolve to that state.
What happens when space and access to sunlight run out? Will they peacefully die so that others may live? Why are not the others doing the same first?
No. There may be non-aggressive races out there, but that will be a philosophical position that they have arrived at when they have fulfilled all their needs (sounds like heaven,, doesn't it?).
If they don't need living space, why are they exploring the galaxy and arriving at our little green speck?