I agree with
*@vinsurin* that a lot of the posts on this thread are very offensive. Replace asexual with gay,or sexually attracted to a different race, and posts suggesting being asexual stops you from being physically healthy or is only because you were traumatised as a child read disgustingly.
I usually agree with lots of the threads on this board and would agree with this one if it was aimed at rainbows or brownies - but guides are for girls aged 10-14, many of whom will be sexually active (if not having full sex) and experiencing sexual or romantic feelings. In which case I don't think it's inappropriate for them to learn about asexuality in the same way it wouldn't be appropriate for them to learn about being gay, bisexuality or lesbian. Of course it is bizarre for a 6 year old to label themselves as asexual but I think it might actually be useful for a 13 or 14 year old who is wondering why she isn't experiencing the same crushes and feelings as her friends and wondering if there is something wrong with her (although according to posters on this board there is!)
As a pp pointed out, we live in an overwhelmingly sexualised world, which can be particularly intimidating for girls. If they are not sure about who they like, saying they think they are asexual for a few years gives them an 'out' from otherwise constant discussion of which you fancy, what you've done with them etc I remember from my own teen years while they figure it out- does it matter? It might actually be a good thing for girls who feel a bit overwhelmed with it all. Unlike being trans nobody is prescribing blockers or surgery to kids who say they are asexual, so what harm is it causing?