(apologies to those who have seen this twice; i sent to the wrong list the first time...)
Gee, I dunno. I always liked having objects in charge of printing themselves. As a programmer, I always knew where to look for the printOn: method and writing "foo printString" is more concise than "foo mirror printString", or whatever it would be. Finally, "meta" anything often confuses beginning programmers because they think it must be more profound than it really is.
Maybe I don't have the context to understand the philosphical issue here but it seems to me that mirrors are a lot like views, which are considered bad (at least in the UI)...