The argument that it follows from name is a red herring. If I create a photo sharing service, should I require you to list a race and justify it by saying that it can be inferred from your photos anyway? To summarize:
name: relevant because it's the center of identity, which is what the product is about.
sex: not a necessary feature of a public profile.
If 99.9% of your users say "um, sure, I wouldn't mind sharing that", and 0.1% say "hell no, I absolutely don't want to share that", then you make it optional unless there's some important reason to not make it so.
name: relevant because it's the center of identity, which is what the product is about. sex: not a necessary feature of a public profile.
If 99.9% of your users say "um, sure, I wouldn't mind sharing that", and 0.1% say "hell no, I absolutely don't want to share that", then you make it optional unless there's some important reason to not make it so.