>>725056839
The Combine see everything as one big organism.
>Attention, ground units — anti-citizen reported in this community. Code: lock, cauterize, stabilize.
>Attention all Ground Protection teams: Judgment waiver now in effect. Capital prosecution is discretionary. Code: amputate, zero, confirm.
>Priority Alert: Nova Prospekt exogen breach… Internal stabilization teams deploy sterilizers in suspected infection blocks A5, A7, B2.
>Anticitizen One engaged. Vance subprime engaged. Expunge… Cauterize and expunge.
Headcrab shells are used like chemotherapy against the cancer that is free humans. Let them continue existing and they'll thrive and spread to other parts of the body. Headcrabs are, essentially, benign as far as the combine are concerned. It isn't impossible for them to kill individual soldiers, but they represent absolutely no significant threat to the whole body. They lack the intelligence/malignance for that.