Well, part of the problem is that we've all accepted that OOP is the best way of modelling the real world, but there is no convincing proof. Maybe experience? I don't know. We do know modularity is valuable. We know OOP is a way of achieving modularity, but is it the best way? And is OOP-like-in-Java the best way of doing OOP?
OOP like many Java (and C++) programmers do it is certainly not what Alan Kay was thinking about (in his own words!). But that's merely an appeal to authority. Maybe Alan Kay was mistaken and the Java folks are right. So the other part of my problem is that OOP is not a well-defined concept at all. I cannot begin to agree OOP is the best way of thinking about the real world until we can determine what OOP is; a definition both a Smalltalk dev and a Java dev can agree on.
I suspect that we've started hitting the issue of "What, actually, is OOP?"