How to easily defeat any argument for God

[Acrobat]

To understand why, let's say, slavery is immoral, all one has to do is ask the f'n slaves if it is good for their well being, and ability to thrive.

You are the one with the subjective morality, because, as Gae Bolga points out above, your morality is based on the subjective whims of your god.

Sure, a slave would likely indicate that slavery isn't beneficial to their well being. Something we might be able to say is objectively true. 

But how about the claim that slave owners ought not do things harmful to the wellbeing of slaves, or others? Is that an objective truth as well. 

Or is that a subjective whim you might subscribe to, but not an objective truth? 

Such claims appear to be built on the unspecified premise, that we ought not to things harmful or detrimental to wellbeing of others and ought to do things beneficial to well being. But is this also an objective truth? If I rejected it, I said no I ought to do whatever I want to do, regardless of whether it's beneficial or harmful to yours or the slaves well being, have I stated something false? Is it akin to claiming the earth is flat? Or just a rejection of some subjective goal/whim?