While Lojban is "logical", human language is not. Or rather, it is, but it follows its own set of (well defined) rules. If Lojban does not follow these rule's, it's not truly learnable, and thus irrelevant. If Lojban _does_ follow these rules, and is genuinely learnable, then it offers little advantage except perhaps a pared down vocabulary that avoids ambiguity and redundancy, and a less flexible morphology and syntax. Assuming the latter, human languages change naturally, in order to facilitate learning and communication, and Lojban would change too, if actually used. Metaphor, ambiguity, imprecision, etc. all are the _products_ of language adapting itself to suit our needs better. So for all the "flaws" of natural languages, they work, and work well, and if Lojban were adopted by people, it would end up looking like a natural language, with all their "flaws". And that's a good thing.