Hofstadter has made an excellent argument on this topic called "A Person Paper on Purity in Language".

Iain Banks, in "Player of Games", also expressed this sentiment pretty well:

"Marain, the Culture's quintessentially wonderful language (so the Culture will tell you), has, as any schoolkid knows, one personal pronoun to cover females, males, in-betweens, neuters, children, drones, Minds, other sentient machines, and every life-form capable of scraping together anything remotely resembling a nervous system and the rudiments of language (or a good excuse for not having either). Naturally, there are ways of specifying a person's sex in Marain, but they're not used in everyday conversation; in the archetypal language-as-moral-weapon-and-proud-of-it, the message is that it's brains that matter, kids; gonads are hardly worth making a distinction over."

My preferred sex-neutral pronoun is "they".