"Inevitably"?
Within just a few thousand years of recorded history, mankind has (for the most part) experienced social progress. Ironically, looking at today's world map, I find most resistant "bubbles" of a more brutal heritage in places where religion is still a major force.
I would disagree. By far the most terrible and bloodiest century in history is the 20th. We see genocides, Total War, the rise of Totalitarianism, a great upsurge in terrorism etc. Violent crime isn't even that much different than people think. 1980s New York had comparable murder rates to Mediaeval London (22 vs 20 per 100 000).
So 'progress' would have to be found in social issues like sexuality, income inequality etc. which are all debatable and in certain cases like acceptance of homosexuality, would be begging the question if considered 'progress'.
Whenever atrocities happen, ideological or religious absolutes are involved. You won't get a person to treat another as subhuman without either convincing him that a Supreme Authority or Higher Ideal demands it, or else establish that those who do not view the world in the same fashion are evil.
Please provide evidence for this statement.
The Nazis merely followed the scientific teaching of their day to its natural conclusion, the germ lying in the concept of 'fitness' as in surival of the fittest. While they were driven by a totalitarian idealogy, it was by no means an Absolute, as can be seen in many areas where they compromised such as allying with Japan or allowing extra-marital affairs. No higher or supreme ideal demanded that untermenschen existed, it was an obvious inference from progressive thinking of their day, the same school of thought that implemented sterilisation programmes for handicapped and mentally ill throughout the west in the 1930s.
Likewise with the Hutu, who were acting out of a sense of having been historically wronged by the Tutsi.
There are other atrocities like the British Concentration camps in the Boer War, Herero genocide in Namibia, the Bataan Death march or the treatment of coolies on Tea plantations which do not fit this characterisation at all. I assume you would say US atrocities in Korea or Vietnam for instance, were committed to try and establish freedom in support of our pervasive western idealogy?
Only with Communism trying to establish 'True Communism' do I perhaps agree, but even here, most atrocities were committed as short term goals beholden to the end point, but not in its name. The Great Leap Forward or Great Ukrainian Famine were both done in a mistaken belief that it would kickstart the economy for the betterment of all, for instance.
Regardless, the worst and most frequent atrocities in the 20th century were committed by fully Atheist or firmly Secular regimes, so the exact groups that had more fluid concepts of Morality. When we base our morality on individual choice, reasoned moral imperatives and interactions between people, it has historically gradually become horrific, so whether this ends up in an idealogy of some form is anyway just unneccesarily introducing an element into the equation. For Idealogy of course emerges, as can be demonstrated in your list of pansexual etc. which is already being defended to the teeth by those who disagree with someone that merely holds other views.
I for one can only see the likes of Raskolnikov or pseudo-Nietschean 'Will to Power' emerging from such 'morality', so I do not consider it moral in any sense of the term.