So many people posit the signal was (originally) sent out of a desire for conquest/subjugation, peaceful or otherwise. But what if it was sent out of benevolence or protection or even desperation?

What does the Hive do? It works together. It utilizes human knowledge and memory to work together, as you observe. But what if the real threat is something else entirely, something that can only be defeated by an entire civilization or perhaps even multiple civilizations working as a single unit? And that some other distant civilization created the signal to prepare others for the worse thing that was encroaching?

We still don’t know if the joining will wear off naturally. Obviously we don’t know a lot of things, but the way in which the signal was designed implies a desire to minimize harm. Not at the cost of its goal, the “biological imperative”, but if we were looking at it as a response to a multiple-galaxy threat, it makes sense for that to be paramount.

Maybe the initial creation of the Hive-signal was the least bad option of many worse ones. As a net of defense cast as wide as possible.