Are you worried that we become cannibals here on Earth, or on Mars?
Mars is an extremely dangerous and deadly environment for us humans. The little air there is on Mars isn't breathable. The pressure is too low to wander outside without a suit. It's about as dangerous as the moon when you think about it.
Now imagine living there, all the bad things that can happen to you. Tiny hole in your suit our house? BAM! No more air, no more pressure. You die. Perhaps the whole base dies. No more water, no more food. Just you in the dark, a couple of dead corpses lying around... Scary indeed.
In extreme scenarios, may humans on Mars go as far as cannibalism to survive? In a super extreme situation... I believe it's possible.