Hypothesizing about a billion year old alien remnant is not Loch Ness monster, it’s just discussing statistics about a phenomena we have no good statistics for - except we know it’s plausible since we already know interstellar space is already populated by two probes launched by a civilization of sentient creatures. I’d say its a topic solidly in the domain of scientific inquiry, but it’s not well defined yet since people trying to discuss it are labeled loonies (reminds me of atom theory and plate tectonics- two phenomena which were prominently ridiculed as well). Of course, ”alien studies” is a domain that is quite hard at the moment-and may always remain so.

And sure, there is lots of crazy talk around the topic. But the fact we have people trying to invent perpetual motion machines does not make every thermodynamicist and machine engineer looney.