In this post I will attempt to succinctly state the anthropic argument against the existence of God (A morally perfect, powerful, and knowledgeable being). I take a lot of inspiration from Mark Walker's piece here, though my discussion will proceed differently. It's basic form is as follows:
(1) If God exists humans would not exist (2) humans exist (3) hence God doesn't exist.
The 2nd premise is uncontroversial, the 1st is where we shall focus our sights.
Imagine this case: You are to procreate a child. We have designed a pill where you can choose what moral, mental, and physical traits your child has. You have two options (a) take a pill where the child in question will have just as much moral, mental, and physical abilities as you do or (b) take another pill where the child in question will be severely morally, mentally and physically deficient to you. In case (a) the human will be, so to speak, average in abilities, but in case (b) the being will have less moral knowledge, be intellectually handicapped, and physically handicapped. Now it seems wrong to take pill (b) since the deficiencies of the child will harm both the child and others; hence you ought to take pill (a). Further if you were to be the child you would clearly wish that your parents chose pill (a) in a case like this.
Lets think of another case, this time from Mark Walker. Suppose humans knowingly create Chumans;
"Chuman’, as this species is known, is created from a human chimpanzee cross. Chumans are mentally and physically challenged in comparison with humans, and have been genetically altered to have a strong propensity for violent outbursts (a propensity they wish they did not have)."
Further these Chumans survive humanity, yet lacking the tools and intellect for modern medicine and agriculture many starve to death. Their history is full of war, disease, starvation, and rape. Wouldn't it be wrong to create such beings? Why create such beings instead of more humans?
In fact there are several real world examples of the results of something like pill (b) and the chumans. There are actual persons who are physically, mentally, and morally handicapped. This causes harm to others due to the lack of moral knowledge and ability, and harm to the person in question who may lose out on many goods of the average human (social, physical, intellectual etc.). If given the choice most parents would choose pill (a), as they ought to.
Hence we can extract the procreation principle like this:
It is wrong for X to cause, knowingly and voluntarily, the procreation of a Y; which is morally, mentally, and physically deficient to X
Using the procreation principle (PP) we can support premise (1). If PP is true God wouldn't create humans since she can do no wrong (being morally perfect and all). Because humans are morally, physically (in terms of ability--since God isn't a physical being), and mentally disabled from God, she wouldn't create such beings.
An Objection Concerning the Impossibility of PP
Suppose it's impossible for God to create creatures that are not morally, mentally, and physically deficient to her. Then one might be tempted to say that PP is false since it is logically impossible for God to create other beings like her in the required senses, yet it is still permissible for her to create beings. I am not inclined to think this is true but suppose it is, lets stipulate that it is logically impossible for God to create other Gods and that it is permissible for God to create a world even so. We then could amend the principle as follows:
It is wrong for X to cause, knowingly and voluntarily, the procreation of a Y; which is UNNECESSARILY morally, mentally, and physically deficient to X
Lets call this idea PP*. In it, unnecessarily means, that X shouldn't create a Y insofar as another Y* could logically be morally, physically, or mentally better off. So PP means X shouldn't create Y's that are deficient, but PP* says that X's can create Y's that are deficient but only as least deficient as possible.
How does this relate to the anthropic argument? Well according too PP* God can only create beings that are least deficient as possible. Do humans fit this criterion? Bluntly stated no they don't. We don't even come close. God could have created Angelic beings with more knowledge, power, and moral goodness. She could have made beings that are good by nature as she is. These beings don't have to be as powerful or knowledgeable as she is, all that is needed is that they be better then humans.
So to the objection that PP is logically impossible hence premise 2 of the argument is false one can reply as such:
No. God could create or sustain other beings with the same mental, moral, and powers as she (even if these beings lack necessary existence or something like that). Further supposing she can't beings like her that in itself is no reason for thinking PP is false. If that were the case God simply wouldn't be morally perfect if she created any world with beings.
Suppose we are mistaken in thinking PP is true, than we can replace PP with PP*. Since there could be better beings than humans the anthropic argument goes through and God isn't justified in creating humans. And as such God as defined does not exist.
I think is one of the strongest arguments against the existence of God. This is probably because it taps into my strongest intuitions of morality and reality. Object away!