It's true, though. Why else would people like hitler feel that they were right to do the horrible things (in my moral opinion) that they did unless they thought it was truly moral. There will always be someone put their who thinks that your morality is wrong, regardless of how right it may seem.
It doesn't matter what anybody thinks, because morality is not subjective. That's the point. Morality is unchanging, our views on morality can simply be right or be wrong.
Well, to really, really simplify it, killing (for instance) isn't wrong or right because you or I think it is wrong or right, it is wrong or right because it just is. So it doesn't matter in the slightest whether any of us think it is wrong or right, because that won't change what it is.