You are confusing moral subjectivism with moral nihilism. If someone says that it is "wrong," but disagrees that it is "objectively wrong" on the grounds of subjectivism, it doesn't follow that they are therefore saying that it's "not wrong.”
Nothing is truly and actually "wrong" if it is "right" for some people.
Try to give it some other label like "subjectivism" doesn't change that.
Again, this thread is about GOD and real "evil"... not about GOD what "most" people think about what they would consider "evil". If we cannot have an absolute standard of morality, why would we even think about applying subjectivist notions to the question of God?
*Who is God’s outside source for morality?
*If God doesn’t need an outside source, why do we?
*How do you know God is an adequate source for morality?
Now these are Good questions.
The answers really come from the definition of "God"... which is not really what this debate is about... although it's probably accurate to say that there's not anything close to agreement about the definition.
God is sometimes described as the "Uncaused Cause." Everything has to be caused by something else... but at some point, you have to get back to a cause that started it all... the one Cause Agent that without any cause itself.
That there must be a "first cause" is logically inescapable. For some, it is the "Big Bang" (or the first of many "Big Bangs"). Others are more comfortable with calling the "First Cause" or the "uncaused Cause" God. Science teaches us a lot, but the scientific method cannot provide us with the answer of which of these two views is correct.
This forum and this thread takes the second view. So, the answer to your first question is that just as God is the "Cause" that needed not outside cause, He's also the morality that needs no outside validation.
That statement is also the answer to your second question. Only the "Uncaused One" can be free from being held accountable, morally, to His/Its "maker." The reason is obvious... because He has no maker.
And that highlights another good point to note... The entire notion of "morality" presumes that there must be some sort of "accountability" for one's actions. If there's absolutely no accountability, then what's the point of calling anything "wrong" or "evil."
The answer to your third question is this... Just as the "Uncaused Cause" is THE source for all other things, so He is the source of anything we call "moral." He is the
measure of morality. What He is... IS what is "moral."
These answers may not satisfy you, but I assert that they are innate in the very definition of the concept of "God."
This is why, for the record, why it is so logically inconsistent to attempt to assert ANY morality in a belief system that denies God and only asserts natural causes for
everything. If everything is an "accident," that happened without any meaning, then morality is just an accidental concept without any meaning.