[dkarapetyan]

Message passing only takes you so far. As soon as you want to start reasoning you will structure your messages into groups and now you're back to what looks suspiciously like classes.

I'm not arguing for one or the other but that extreme late-binding as espoused in much of the smalltalk way of doing OO only takes you so far. Static reasoning about program structure is helpful and just message passing alone does not give you enough structure to do that.