It's not an inconsistency, it's an axiom: https://en.m.wikipedia.org/wiki/Axiom_of_extensionality
OP's other post's comment is related https://news.ycombinator.com/item?id=19265632
I am not even talking about comparing sets. I am talking about comparing infinite-precision floats to themselves.
Any system that does it in O(1) is broken.