You don't believe it, because you consider some acts fundamentally unacceptable, in your moral framework.
That doesn't have any bearing on other people's moral frameworks, in which relativistic calculations may be the right thing to do.
That doesn't have any bearing on other people's moral frameworks, in which relativistic calculations may be the right thing to do.
It becomes at best a statement of opinion, and at worst it can be taken as dismissive of the values of others.
I don't believe this is a very useful property of a conversation which is about trying to understand how the world squares with opinions that people can hold.