All I can say is, it must have been a HUNGRY person, that first person that ate a crab, shrimp, or lobster.

A couple of years ago, as a hobby, I had a large chilled saltwater aquarium, and I stocked the whole thing with stuff only from Puget Sound. Once you watch what crabs and shrimp do day after day, you sort of lose your appetite for them... believe me.

Put some cooked, cleaned, cracked crabmeat in front of me, though, and I still can't resist it.
I've yet to explore the taste differences between cooking pre and post cleaning, I've always just cleaned them before cooking, because, like others have said, you can fit way more crabs in the cook pot. That smelly foam is sort of disgusting, too, but hell, so is lots of other stuff we eat all the time.

-N.