> "The biggest problem from my PoV is that people seem like they are always absolutely sure that the contemporary understanding of morals is actually correct, unlike the primitive beliefs of the past, and that there's nothing left to challenge."
If they claim to be on the left, point out to them that that type of worldview is actually a form of conservatism. Quoting from Wikipedia, "Traditionalist conservatism places a strong emphasis on the notions of custom, convention, and tradition." and note that "customs
[and] convention" is the same as the "social norms" argument trotted out by the modern left to defend their activities.
If what you are trying to say is that what's new and modern today will someday, probably sooner then later, be old and "normed" tomorrow, then yes...absolutely this will be the case.
This understanding is the basis of the Right's "slippery slope" argument...that in normalizing behaviors today that yesterday were considered "wrong", they tomorrow can we expect ever more and more outrageous behaviors to follow this same template?
It is my belief that many, if not most, people believe themselves to having never changed their opinion, even though they have done so many times. To admit to yourself that you once were wrong is to admit that you were imperfect; it is easier to believe that you have always thought what you currently believe.
And, consequently, if you have never changed opinions, your current understanding of things must therefore be correct and unchanging, and policy can be written and implemented with this assumption.
For the right, conservatism is their schtick so there's no criticism to be made. One can (and should) disagree with their beliefs but the contents of the box is exactly what the label says it is, so to speak.
It's the new left who claim to be on the side of liberals but whose continue to espouse illiberal beliefs that need to be called out as to what they are.
If they claim to be on the left, point out to them that that type of worldview is actually a form of conservatism. Quoting from Wikipedia, "Traditionalist conservatism places a strong emphasis on the notions of custom, convention, and tradition." and note that "customs [and] convention" is the same as the "social norms" argument trotted out by the modern left to defend their activities.