Does that mean a strong Nihilist could, much like God, just say something and decree it as moral, regardless of what it is?
I've never agreed with the assertion that morals are that wonky or that they need a concrete point of reference. Human suffering doesn't change, nor does the group dynamics that we evolved in. People can convince themselves of anything given time, and legitimate arguments can be made to make something moral in certain context, such as going to war for good reasons.
I realize it's impossible to discuss morality in black and white. It's a highly philosophical discussion. But I don't believe that anyone can simply say X and have X be true, or that if enough people were to believe X is right and moral, that would make X right and moral. It's by no means black and white, but it's not a damn rainbow where you can choose whatever.