[bugzz]

If they had "no problem" cannibalizing their offspring, they'd quickly go extinct! In reality, cannibalizing of offspring only occurs in particular circumstances - if conditions are poor enough that most of the young won't survive anyway, for example. In which case their instincts kick in to cannibalize as a way to recoup the energy and try again at a better time. If conditions are right there will instead be a strong instinct to protect the egg sack / young.