It's like Kurzweil describing the exponential curve of self-replicating AI leading to the Singularity and infinite machine intelligence... it's an elegant, mathematically self-evident solution that just happens not to correlate with reality.
It has literally nothing to do with the nature of whatever aliens might build these hypothetical machines. The only requirement is that some group with modest resources and marginally better technology than us wants to do it.
> It's like Kurzweil describing the exponential curve of self-replicating AI
A little early to try and refute that, don't you think? We're still on an exponential production trend.
That's not "modest resources and marginally better technology than us", that's perilously close to being magic. Not even viruses, the most aggressive and efficient self-replicators we know of, have managed to consume all the biomass on the planet, or could reasonably be expected to do so.
This is a false premise. It doesn't have to do anything this fancy.
You can expect that any given asteroid is likely to have a certain amount of iron, carbon, silicon, nickel, etc.
In almost any solar system, you can mine the materials needed for construction very easily. Solar gives you enough energy to do (slow, deliberate) resource extraction from asteroids.
As for propellant and reaction mass, we already know nuclear explosions work excellently. Unfortunately, based on analysis of meteors we don't expect asteroids to have great heavy-metal concentrations; on the order of 10ppb for Uranium. This presents a challenge, but not an insurmountable one; it just means that you'll probably want to get explosive materials closer to the center of the system.
> Not even viruses, the most aggressive and efficient self-replicators we know of, have managed to consume all the biomass on the planet, or could reasonably be expected to do so.
This is true, but 100% irrelevant to the challenges of creating space-based manufacturing capable of reproducing all its own components.
It doesn't have to be "self replicating drones." It could be inert bullets, arrow heads, sharp sticks, carefully arranged electromagnetic retro-reflectors.
Drones are a fad. The paradox doesn't require an alien implementation of drone technology, self replicating, autonomous, or what have you.
The concept of autonomous machines is a fad?
As technology advances, autonomous machines may very likely grow beyond the definition/parlance of a "drone" (machinery designed and dedicated only to perform specific tasks) into more powerful forms of intelligence.
At that point, such machinery graduates beyond the definition of an artifact (a possession held in the ownership of higher-order life), and one might speculate whether it represents a form of life unto itself, or where one might draw such a boundary.
Either way, such sentient machinery (read: not drones) might not be bound by geological/astronomical timescales, outlasting its inventors possibly permanently, but still represents a component of the Fermi Paradox. If such things are possible, where are they?
Yeah, you're just making shit up. The first machine intelligence in pop culture can be found in https://en.m.wikipedia.org/wiki/R.U.R. (the origin of the phrase "robot"). Non-sentient autonomous machines are even older. https://en.m.wikipedia.org/wiki/Golem Sci-fi authors have been talking about modern-looking self-replicating machines for decades.
Maybe you have some weird definition of a drone? Drones in common parlance have come to be associated with any robotic vehicle, and are used in technical parlance to refer to a huge variety of autonomous or semi-autonomous machines.
It's pretty clear that the "drones" the GGP is referring to are self-replicating autonomous machines, which could, with a relatively extremely small initial mass-energy investment, visit every solar system in the galaxy in a matter of megayears. It doesn't require leadership or social approval or whatever you're talking about; anyone with technology marginally more advanced than what we have could do it with the equivalent of a few tens of billion dollars of machinery. The more advanced you are, the cheaper it gets. It's very odd that we haven't seen anything like that yet.