It's only daft to those people who have either not considered or not properly researched the variety and richness of human experience. It's clear, from anyone who has read about, for example, many other cultures, that human identity cannot, and should not, be viewed as so clearly defined as "male" and "female", corresponding purely to biological concerns. It's sad that we're talking about this in the context of a convicted murderer, whose right to respect is already on shaky ground as it is, but it should be possible to separate your contempt for them for that horrific crime, to your thoughts of their personal identity.
The fact is that gender identity is not so easily determined as staring at someone's crotch. Human experience since time immemorial has taught us this -- just because you personally didn't notice in the 50s doesn't mean it wasn't true, but it was clearly better-hidden.
As for the remark about wanting to be a singer, there's no comparison, and that's best ascribed to wilful ignorance rather than a serious attempt to contribute to discussion.