So the right to life is part of the social contract? We need each other, therefore we will agree not to kill each other. There are species that are cannibalistic though. They eat the "slow" or inferior ones of their own offspring, to reserve time and effort only to those that they deem worthy. When humans do something akin to this we throw a hissy fit and designate it the term fascism. But judging by how many we are now competing for the earth's limited resources I'd say the time is ripe for some thinning out of the population.