>no one really knows if they even recover down there

It seems like it would be pretty easy to find out. I guess there isn't much motivation to open that can of worms.

It is tricky to get correct information here, as many of the organization that are related to the conservation of the species are funded by the main producers of LAL based endotoxin tests (and hence bleeders, or procurers of Horseshoe crab blood).

At this point, Horseshoe crabs are critical infrastructure in qualityquality control for Pharma and medtech.

Source: Co-founded biotech startup in the horseshoe crab space that had to fold.

Horseshoe crabs aren't crabs. They're distantly related, although both are arthropods. Not much brain activity going on there. But honestly pain and suffering are so hard to nail down outside the tetrapods. I'd say the fact that until we started harvesting their blood more sustainably, they pretty much all died is enough of a reason to harvest them more sustainably, regardless of how we define the ability to suffer. They're an important food source for a lot of different animals and we shouldn't be damaging their numbers when we can get the same product without killing them.

Also, they like to hump fishermen's boots during breeding season, which is absolutely hilarious and I think well worth preserving the species.

Presumably you aren't abducted by creatures beyond your comprehension who start draining your blood without asking!

I don't suspect the crabs have any real understanding of what's happening so the morality of it is ambiguous, but your analogy isn't really analogous.