Why was a goat an acceptable offering for sin, monsieur?
From ISBE
It could be used because it was one of the clean animals.Just as the kid was often slaughtered for an honored guest (Jdg_6:19; Jdg_13:19), so the kid or goat was frequently taken for sacrifice (Lev_4:23; Lev_9:15; Lev_16:7; Num_15:24; Ezr_8:35; Eze_45:23; Heb_9:12). A goat was one of the clean animals (sēh ‛izzı̄m, Deu_14:4). In Daniel, the powerful king out of the West is typified as a goat with a single horn (Dan_8:5). One of the older goats is the leader of the flock. In some parts of the country the goatherd makes different ones leaders by turns, the leader being trained to keep near the goat-herd and not to eat so long as he wears the bell. In Isa_14:9, “.... stirreth up the dead for thee, even all the chief ones of the earth,” the word translated “chief ones” is ‛attūdh, “he-goat.” Again, in Jer_50:8, we have “Go forth out of the land of the Chaldeans, and be as the he-goats before the flocks.”