First of all, dissecting anything that comes from those companies is supporting their mass murders of cats and dogs, even if you don't think crayfish matter.
This "It's already dead," argument is getting REALLY old. I've been told that about 25 times already, just in the last two days. The point is, by going along with the dissections you agree that was it going on is A-ok, and it's NOT.

Here's some of the cats (after they've gone through the abuse and painful death) that the same company that sends crayfish and worms and frogs and fetal pigs to your shcool -