On Lust in the context of sin and desire.

 There is only meaning because you believe, because you believe there is meaning, belief being the foundation of meaning, if Humanity was made exactly in God's image and the cardinal sin of lust is chemically involuntary within the human body the thought of lust being sinful is preposterous. 

Mathew 28: "But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart."

Meaning you wouldn't have to act on such thoughts for them to be sins.

The buddha says you should not desire, and many monks mutilate themselves willingly becoming eunuchs.

I see this as unnecessary unless your goal is to eliminate desire from your heart and try to escape reincarnation, but this is silly as you desire to be free of Desire.

If everyone was asexual the human race would end, would that be more pure because no more sin can be committed by humanity?

What marks the difference between healthy sexuality and unhealthy sexuality if it's being enjoyed by both parties as Sodom and Gomorrah. I would argue that its unhealthy when both parties aren't entirely enjoying it and it goes into the territory of sadomasochism but is it really a bad thing?

I would say non-consentual sex is the only variety of lust that should be considered sinful.