I think if you could undergo a perfect and reversible sex change operation as easily as changing your clothes, it would become simply a matter of fashion - but with that kind of technology, changing your sex would be one of the least interesting things you could do, and new controversies would arise: for example, is it ethical to modify your body to look exactly like someone else’s body? And how far can you go with body modification before it stretches credulity to identify as a human, and what does that mean for the concept of human rights?