You're right, you cannot refuse somebody just because they're male, but the point of this entire thread is you should be able to as long as it's a statistically proven fact the other gender isn't normally as good at the job. If a company wants to hire somebody quickly, and they're more likely to get better performance out of one gender, they should be allowed to specify the gender.

As long as there is no prejudice, there isn't sexism.

Sexist: characterized by or showing prejudice, stereotyping, or discrimination, typically against women, on the basis of sex.

Prejudice: preconceived opinion that is not based on reason or actual experience.