Nothing So Cruel, Wasteful and Destructive as the Norm
Take a look back at history, and see what has been endorsed, defended and welcomed as the norm of behavior in human society: violence, infliction of pain, incredible delusion, victim groups and mass murders (sanctified by religious hierarchies or the states that substitute for their role), enforced beliefs, abandonment to death, and much more.
Then look at today. The only things to have changed are the degree and the details - and don't kid yourself that the degree is all that great in the grand scheme of things. Most likely you hold one or more incredible delusions and consider a broad range of murders sanctioned, on the basis that this is "normal," for all that you're what would be described as a principled, kind, upright sort of person. It is entirely possible that I do also.
We humans are deeply flawed in this respect. Start out with decent-at-the-small-scale folk you'd be happy to have as neighbors and you'll wind up with a society that advocates and defends the most outrageous, irrational, cruel and terrible beliefs and actions. But there's no such thing as "society" - only individuals making individual choices. It is those decent-at-the-small-scale individuals who advocate, defend and ultimately carry out cruel and destructive actions.
I leave it up to the reader to fill in their personal specifics, but I'm sure you know where the worst is from my point of view: the acceptance and defense of degenerative aging, and the acceptance and defense of death and suffering due to aging. More than 100,000 people die due to the results of aging - of accumulated cellular damage that we are doing too little to try and repair - each and every day. Hundreds of millions suffer in one way or another. Every day, day in and day out, a tide of death that beggars the imagination. Think of that a moment.
Other human cruelties and irrational beliefs fade into the background in comparison to the defense of age-related suffering and death in an era of accelerating biotechnology and medical research. We are very close to a time in which aging can be repaired - but as for any goal, it will only come to pass if the desire is there. Yet the vast majority of people do nothing, and accept or support the suffering and death that is everywhere and all around.