It sounds like we both want to say that the holocaust is objectively wrong, not merely subjectively wrong. I don't know where best to start but I do think knowledge and problem solving are key to the answer.

There is objective truth about the physical world, and we work towards it by error-correcting and replacing our bad explanations with better explanations. Errors and bad explanations cause us problems, and we create knowledge to solve them.

Moral problems like the holocaust also require knowledge to solve. With more knowledge, we could have stopped the holocaust sooner. We can't just embrace ignorance and unreason and hope for the best, we need to create a continuous stream of knowledge to solve the continuous stream of problems we face.

You can't just commit to any subjective moral values you feel like and hope to have continual success in knowledge creation. Unbounded knowledge creation requires commitment to moral values such as tolerance, openness to criticism and change, and respect for truth. Blind obedience to authority, rigid acceptance of dogma and commitment to infallible final solutions are all morally bad and limit our ability to make continual progress.