How many species are basically the same if you completely ignore differences in size, texture, color, and behavior? If you squint right, we're just apes in suits. It's almost like all those small differences add up to an outsize impact.
"ABC" and "Abc" are the same, if we ignore case, and so it goes.
You can't fix it with absolute equivalence, because absolute equivalence requires that some entity A is only equal to that same entity A, and no other entity; that is then inapplicable if we want to use equivalences for division into classes that have more than one member.
I often wonder how anyone could dispute out origin when you look at a chimpanzee then look at a human. The similarities are incredibly striking.