Argument from Conscience

[Neo-Scholastic]

One group says the bible, another only the new testament, a third the Quran…So, ultimately, the theist is left with subjective opinion… An objective morality that is inaccessible is no better than no morality at all.

What you are basically saying is that imperfect knowledge is no better than no knowledge at all. It would be like saying that because there are many different languages you cannot know anything about linguistics. Subjective moral reasoning, despite its flaws, has as its object some source of moral authority. Religious texts are an instrumental source of authority, tools religions use to gain knowledge of God, who is the ultimate and objective source of authority.