There is something monstrously arrogant in claiming that one gets one's morality from God.
The speaker is saying that, "The mind that gave birth to these moral principles is the mind of an all-knowing, morally perfect being." Of course, the mind that gave birth to those ideas is the speaker's mind, thus yielding the implication that the speaker's mind is the mind of an all-knowing morally perfect being.
One of the costs of this way of thinking is that it leaves no room for debate - no room for the speaker to say, "Ooops, I guess I was wrong." Because, clearly, an all-knowing, morally perfect mind cannot be wrong!
So, the arrogant and presumptuous individual who claims that he gets his morality from God locks in the results of his own human failings. He denies that they exist and, in doing so, shuts down the possibility that knew knowledge and understanding might correct his original errors.
On the issue of abortion, those who falsely claim that they get their morality from an all-knowing morally perfect mind have made a mistake. They have locked this mistake in concrete and they now devote huge amounts of resources - resources that could have gone to doing good in the world - pursuing this mistake.
On the issue of abortion, a being that has no desires has no interests. A being that has no interests cannot be harmed in any morally significant way. Any sacrifice that is made for the sake of an entity that has no interests is a wasted sacrifice. The person who makes the sacrifice is forced to be made worse off, and nobody benefits.
Now, after a while a conceptus will develop into a being that has desires. At that time, the being has morally relevant interests and there are legitimate prescriptions against what may be done to that person. But not before.
To illustrate this, let is compare and contrast the effect of aborting a fetus that has no interests to the decision not to conceive that same person. We have a couple with a choice to make. They can abstain from having sex (and, in doing so, prevent a particular conception), or they can have sex and abort the fetus that results before it acquires any morally significant interests.
In the case of abortion, we are often told to imagine some young child that would have existed if the abortion had not taken place - a young child at play (meant to generate an emotional response void of all reason).
We are told that the absence of this child is reason to condemn abortion and to hold that those who have or perform abortions have committed murder.
However, we can apply this same argument toa refusal to conceive. Take the same young child and ask, "What would have happened if that child's parents had decided to abstain from sex - if they had acted in ways that thwarted the conception of that future child." I am not talking about the use of birth control (though the argument applies). I am talking about the decision not to have sex.
The child has just as much of a reason to be grateful that the parents had sex as to be grateful that the parents did not have an abortion. If the act of aborting the fetus is murder because of the future child that does not exist. Then, the act of failure to conceive is also murder, because it brought resulted in the same non-existence of a future child.
We should fill the world with as many people as possible. As long as the planet can hold one more young child, we have committed a sin comparable to murder if we fail to act to fill that spot with a young child.
Monstrously arrogant people who attribute their morality to God give themselves permission to ignore any argument that they could be mistaken. "You have your puny and finite mind up against the all-knowing, morally perfect mind that invented these moral principles. You are going to lose by default. In fact, we can begin with the assumption that you are mistaken - because you must be - and work from there to find the source of your obvious error."
The error, of course, is that of the monstrously arrogant person who thinks that his ideas are the ideas of an all-knowing, morally perfect being that are incapable of error. They are, in fact, the ideas of a person with very limited knowledge and who falls far short of moral perfection who likes to think that he cannot be mistaken - and who then invents a way of preventing the possibility of error.
Of course, people who make this argument also claim, "No, I admit that I am a fallible human being with limited wisdom and with moral failings." So, one might want to argue that I am mistaken in calling such a person monstrously arrogant.
However, he is still taking the ideas that came from his own mind as the ideas of an all-knowing, morally perfect entity. He is still looking at these principles and saying, "WOW! Those ideas are so brilliant! So perfect! They must have come from an all-knowing, morally perfect being!" At this point we merely need to add the fact that they came from the speaker himself, and we get the monstrously arrogant conclusion, "Then I must be an all-knowing, morally perfect being who simply made a mistake in thinking I was a fallible mortal."
This blog is written by a mortal human being. It is written by a person who is capable of making mistakes. In fact, I have repeatedly asserted, and I will assert again, that this blog contains at least one false statement. I do not know which statement that is, but I know that it is in here somewhere. You, the reader, is not to take anything that I have written as gospel truth. With every sentence that you read, you must be aware that it may well be one of those statements that are certain to exist in this blog that is false, and to read it and examine it with a healthy bit of skepticism.
This is the difference between a person who recognizes the fact that his ideas are the ideas of a mere mortal and subject to error, and the person who thinks that his ideas come from an all-knowing and morally perfect mind (his own, as a matter of fact) that is incapable of error. It is the difference between inviting readers to question what the author says, and demanding that the reader accept everything that the author says without question.