Are you sure about the "raw meat" part?
I have only seen two "settler" corpses in any of my build zones (plenty of other ones out and about the Wastelands of course . . .). While it is possible that one or both of these were killed by hostile NPCs (or friendly fire from other settlers), it seems more likely to me that they were killed by either me or more likely my turrets and moreover, WHILE I was there.
In the absence of any proof that settlers "Protected" status is changed to "Normal" while the player is not in the cell, I think it makes more sense from a programming standpoint that their "Protected" status remains in effect all the time. I suppose this could be confirmed by looking at the files, but I have yet to get into that, and don't want to get into the habit of using non-GECK tools to fiddle with the files.
I think the way it works is: if the sole survivor does not respond to the "help" alert in a timely fashion, there is a script that is run that causes damage to crops or defenses. It may actually delete walls too, as I've noticed a couple settlements where sections of walls went missing. I have my doubts that settlers are killed, though they may be.
I am not positive yet, but I do not think it matters. Provisioners and allied settlers seem to have the "Protected" status, which means they can only die as a result of damaged caused by the player. This includes turrets that have been placed by the player though.