I don't see how that has any bearing really. Moses is not a murderer, Moses never killed anyone that was innocent. Moses sin was not a sin unto death, but it was he did not give glory to God because the people provoked him in the wilderness to give them water from a rock. For this Moses paid his punishment which was that he would not be allowed to enter the Promised Land.
I know that many groups try to make this claim to sound wise, but really they're unlearned. They are incorrect, not all sins are the same, there are sins unto death and there are sins that are not unto death. The Bible is very clear about this in both the OT and the NT. Yes, you can be forgiven though of either a sin not unto death or a sin unto death, but you have to repent, and if you're truly repentful you're not going to be doing, excusing, or defending those things. It's a war, there's two kingdoms, you can only fight for one and defend one.