Bleeding horseshoe crabs to death is not an acceptable practice in the U.S.
The volume of blood taken is actually quite small, as most of the material in the collection jars is anticoagulant.
It may look uncomfortable to us humans, but keep in mind that horseshoe crabs are not human. What’s normal for the spider is chaos for the fly. Granted, it would be kinda weird to be hoisted from your home by a giant ape and forced into a blood drive. It’s done as gently as possible though.