Transhumanism, when it is an actual "intellectual and cultural movement" instead of just a decent plot hook for a novel, is a ridiculous dodge. My objections, though, are not because of the morality of what we might do, which seems to be the bone of contention in the all of the criticisms listed in Wikipedia; i think that's all a bunch of handwringing nonsense. Instead, the real problem with transhumanism is that it turns away from the problems that we have now by thinking about how we can solve them in the future. We should be thinking about how to solve these problems now. How can one think about moving beyond one's humanity when we don't yet know how to effectively be human?
To call yourself a transhumanist is to reveal yourself as the worst sort of elitist asshole, because you're trying to solve your personal inconveniences with technology that doesn't exist. There are people all over the world dying because they have no clean water; societies still haven't figured out how to have representative leadership that scales as populations increase and that discourages leaders from making a career out of pulling strings; there's (a possibly imagined renaissance of) fundamentalist fuckheads around the world who are trying to stamp out critical thinking; and much more, at the root of all of which lies this: we don't know how to teach our kids how to learn and what to learn in order to make tomorrow better. So when you talk to me about the Singularity, i'll probably just tell you to fuck off, because there's no way we'll generate artificial intelligence worth a damn when we barely have a clue what natural intelligence is or how it works (and i'm talking wetware here). Stop wanking to your fantasy of a nanotech-enhanced brain, and spend that energy figuring out how to get along with your neighbor.