tl;dr
It's estimated that 1% of the world's population is asexual, although research is limited.
"Theoretically the absence of sexual desire shouldn't be a problem," says Dr Tony Bogaert, an associate professor at Brock University in Ontario who specialises in research into asexuality. "But ours is a media which suggests hypersexuality is the norm. Potentially, asexuality has become a 'problem' as it became more visible, and in a sense it's become the new stigma."