If masturbation was wrong, it wouldn't be so conveniently located.
From a biblical perspective, keep in mind that the story of Onan is usually misinterpreted, it has nothing to do with masturbation. Onan's sin was to fail to live up to his obligation to impregnate his sister-in-law.
Believing in sin is fucking ridiculous. If everyone denied what the 'good book' considers sin, we would all be psychotic miserable human beings...or behave like priests; which isn't all that different.
Believing in sin is fucking ridiculous. If everyone denied what the 'good book' considers sin, we would all be psychotic miserable human beings...or behave like priests; which isn't all that different.